How to get relative path from absolute path

Question

There s a part in my apps that displays the file path loaded by the user through OpenFileDialog  It s taking up too much space to display the whole path  but I don t want to display only the filename as it might be ambiguous  So I would prefer to show the file path relative to the assembly exe directory   For example  the assembly resides at C  Program Files Dummy Folder MyProgram and the file at C  Program Files Dummy Folder MyProgram Data datafile1 dat then I would like it to show   Data datafile1 dat  If the file is in C  Program Files Dummy Folder datafile1 dat  then I would want    datafile1 dat  But if the file is at the root directory or 1 directory below root  then display the full path    What solution would you recommend  Regex   Basically I want to display useful file path info without taking too much screen space   EDIT  Just to clarify a little bit more  The purpose of this solution is to help user or myself knowing which file did I loaded last and roughly from which directory was it from  I m using a readonly textbox to display the path  Most of the time  the file path is much longer than the display space of the textbox  The path is supposed to be informative but not important enough as to take up more screen space   Alex Brault comment was good  so is Jonathan Leffler  The Win32 function provided by DavidK only help with part of the problem  not the whole of it  but thanks anyway  As for James Newton-King solution  I ll give it a try later when I m free

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It s a long way around  but System Uri class has a method named MakeRelativeUri  Maybe you could use that  It s a shame really that System IO Path doesn t have this

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This should work   private string rel string path      string   cwd    new Regex          Split Directory GetCurrentDirectory       string   fp     new Regex          Split path      int common   0     for  int n   0  n  lt  fp Length  n          if  n  lt  cwd Length  amp  amp  n  lt  fp Length  amp  amp  cwd n     fp n           common                 if  common  gt  0        List lt string gt  rp   new List lt string gt          for  int n   0  n  lt   cwd Length - common   n            rp Add                   for  int n   common  n  lt  fp Length  n            rp Add fp n               return String Join      rp ToArray         else       return String Join      fp

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Use   RelPath   AbsPath Replace ApplicationPath

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I m using this   public static class StringExtensions          lt summary gt        Creates a relative path from one file or folder to another         lt  summary gt         lt param name  absPath  gt Absolute path  lt  param gt         lt param name  relTo  gt Directory that defines the start of the relative path  lt  param gt          lt returns gt The relative path from the start directory to the end path  lt  returns gt    public static string MakeRelativePath this string absPath  string relTo            string   absParts   absPath Split Path DirectorySeparatorChar         string   relParts   relTo Split Path DirectorySeparatorChar             Get the shortest of the two paths       int len   absParts Length  lt  relParts Length             absParts Length   relParts Length            Use to determine where in the loop we exited       int lastCommonRoot   -1        int index            Find common root       for  index   0  index  lt  len  index                      if  absParts index  Equals relParts index   StringComparison OrdinalIgnoreCase                 lastCommonRoot   index            else              break                    If we didn t find a common prefix then throw       if  lastCommonRoot    -1            throw new ArgumentException  The path of the two files doesn t have any common base               Build up the relative path       var relativePath   new StringBuilder              Add on the          for  index   lastCommonRoot   1  index  lt  relParts Length  index                    relativePath Append                relativePath Append Path DirectorySeparatorChar                     Add on the folders       for  index   lastCommonRoot   1  index  lt  absParts Length - 1  index                    relativePath Append absParts index            relativePath Append Path DirectorySeparatorChar                 relativePath Append absParts absParts Length - 1           return relativePath ToString

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I have used this in the past        lt summary gt      Creates a relative path from one file     or folder to another       lt  summary gt       lt param name  fromDirectory  gt      Contains the directory that defines the     start of the relative path       lt  param gt       lt param name  toPath  gt      Contains the path that defines the     endpoint of the relative path       lt  param gt       lt returns gt      The relative path from the start     directory to the end path       lt  returns gt       lt exception cref  ArgumentNullException  gt  lt  exception gt  public static string MakeRelative string fromDirectory  string toPath      if  fromDirectory    null      throw new ArgumentNullException  fromDirectory       if  toPath    null      throw new ArgumentNullException  toPath       bool isRooted    Path IsPathRooted fromDirectory   amp  amp  Path IsPathRooted toPath       if  isRooted          bool isDifferentRoot    string Compare Path GetPathRoot fromDirectory   Path GetPathRoot toPath   true     0        if  isDifferentRoot        return toPath         List lt string gt  relativePath   new List lt string gt       string   fromDirectories   fromDirectory Split Path DirectorySeparatorChar      string   toDirectories   toPath Split Path DirectorySeparatorChar      int length   Math Min fromDirectories Length  toDirectories Length      int lastCommonRoot   -1        find common root   for  int x   0  x  lt  length  x            if  string Compare fromDirectories x   toDirectories x   true     0        break       lastCommonRoot   x         if  lastCommonRoot    -1      return toPath        add relative folders in from path   for  int x   lastCommonRoot   1  x  lt  fromDirectories Length  x            if  fromDirectories x  Length  gt  0        relativePath Add                  add to folders to path   for  int x   lastCommonRoot   1  x  lt  toDirectories Length  x            relativePath Add toDirectories x              create relative path   string   relativeParts   new string relativePath Count     relativePath CopyTo relativeParts  0      string newPath   string Join Path DirectorySeparatorChar ToString    relativeParts      return newPath

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NET Core 2 0 has Path GetRelativePath  else  use this        lt summary gt      Creates a relative path from one file or folder to another       lt  summary gt       lt param name  fromPath  gt Contains the directory that defines the start of the relative path  lt  param gt       lt param name  toPath  gt Contains the path that defines the endpoint of the relative path  lt  param gt       lt returns gt The relative path from the start directory to the end path or  lt c gt toPath lt  c gt  if the paths are not related  lt  returns gt       lt exception cref  ArgumentNullException  gt  lt  exception gt       lt exception cref  UriFormatException  gt  lt  exception gt       lt exception cref  InvalidOperationException  gt  lt  exception gt  public static String MakeRelativePath String fromPath  String toPath        if  String IsNullOrEmpty fromPath   throw new ArgumentNullException  fromPath        if  String IsNullOrEmpty toPath     throw new ArgumentNullException  toPath         Uri fromUri   new Uri fromPath       Uri toUri   new Uri toPath        if  fromUri Scheme    toUri Scheme    return toPath       path can t be made relative       Uri relativeUri   fromUri MakeRelativeUri toUri       String relativePath   Uri UnescapeDataString relativeUri ToString          if  toUri Scheme Equals  file   StringComparison InvariantCultureIgnoreCase                 relativePath   relativePath Replace Path AltDirectorySeparatorChar  Path DirectorySeparatorChar              return relativePath

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Way with Uri not worked on linux macOS systems  Path   var www root  can t be converted to Uri  More universal way - do all by hands   public static string MakeRelativePath string fromPath  string toPath  string sep              var fromParts   fromPath Split new                         StringSplitOptions RemoveEmptyEntries       var toParts   toPath Split new                         StringSplitOptions RemoveEmptyEntries        var matchedParts   fromParts          Zip toParts   x  y    gt  string Compare x  y  true     0           TakeWhile x   gt  x  Count         return string Join     Enumerable Range 0  fromParts Length - matchedParts           Select x   gt         sep                 string Join sep  toParts Skip matchedParts                PS  i use     as a default value of separator instead of Path DirectorySeparatorChar  because result of this method used as uri in my app

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If you re sure that your absolute path 2 is always relative to absolute path  just remove the first N characters from path2  where N is the length of path1

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Play with something like   private String GetRelativePath Int32 level  String directory  out String errorMessage            if  level  lt  0    level  gt  5                errorMessage    Find some more smart input data               return String Empty                                                          while  level    0                directory   Path GetDirectoryName directory               level -  1                                                          errorMessage   String Empty          return directory          And test it   Test      public void RelativeDirectoryPathTest             var relativePath               GetRelativePath 3  AppDomain CurrentDomain BaseDirectory  out var errorMessage           Console WriteLine relativePath           if  String IsNullOrEmpty errorMessage     false                Console WriteLine errorMessage               Assert Fail  Can not find relative path

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If you re sure that your absolute path 2 is always relative to absolute path  just remove the first N characters from path2  where N is the length of path1

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If you are using  NET Core 2 0  Path GetRelativePath   is available providing this specific functionality           var relativeTo     C  Program Files Dummy Folder MyProgram           var path     C  Program Files Dummy Folder MyProgram Data datafile1 dat            string relativePath   System IO Path GetRelativePath relativeTo  path            System Console WriteLine relativePath              output -- gt  Data datafile1 dat    Otherwise  for  NET full framework  as of v4 7  recommend using one of the other suggested answers

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If you know that toPath is contained by fromPath then you can keep it simple  I ll leave out the asserts for brevity   public static string MakeRelativePath string fromPath  string toPath           use Path GetFullPath to canonicalise the paths  deal with multiple directory seperators  etc      return Path GetFullPath toPath  Substring Path GetFullPath fromPath  Length   1

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If you have a readonly text box  could you not not make it a label and set AutoEllipsis true   alternatively there are posts with code for generating the autoellipsis yourself   this does it for a grid  you would need to pass i the width for the text box instead   It isn t quite right as it hacks off a bit more than is necessary  and I haven t got around to finding where the calculation is incorrect  it would be easy enough to modify to remove the first part of the directory rather than the last if you desire   Private Function AddEllipsisPath ByVal text As String  ByVal colIndex As Integer  ByVal grid As DataGridView  As String      Get the size with the column s width      Dim colWidth As Integer   grid Columns colIndex  Width       Calculate the dimensions of the text with the current font     Dim textSize As SizeF   MeasureString text  grid Font       Dim rawText As String   text     Dim FileNameLen As Integer   text Length - text LastIndexOf          Dim ReplaceWith As String               Do While textSize Width  gt  colWidth           Trim to make room for the ellipsis         Dim LastFolder As Integer   rawText LastIndexOf      rawText Length - FileNameLen - 1           If LastFolder  lt  0 Then             Exit Do         End If          rawText   rawText Substring 0  LastFolder    ReplaceWith   rawText Substring rawText Length - FileNameLen           If ReplaceWith Length  gt  0 Then             FileNameLen    4             ReplaceWith              End If         textSize   MeasureString rawText  grid Font      Loop      Return rawText End Function  Private Function MeasureString ByVal text As String  ByVal fontInfo As Font  As SizeF     Dim size As SizeF     Dim emSize As Single   fontInfo Size     If emSize   0 Then emSize   12      Dim stringFont As New Font fontInfo Name  emSize       Dim bmp As New Bitmap 1000  100      Dim g As Graphics   Graphics FromImage bmp       size   g MeasureString text  stringFont      g Dispose       Return size End Function

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NET Core 2 0 has Path GetRelativePath  else  use this        lt summary gt      Creates a relative path from one file or folder to another       lt  summary gt       lt param name  fromPath  gt Contains the directory that defines the start of the relative path  lt  param gt       lt param name  toPath  gt Contains the path that defines the endpoint of the relative path  lt  param gt       lt returns gt The relative path from the start directory to the end path or  lt c gt toPath lt  c gt  if the paths are not related  lt  returns gt       lt exception cref  ArgumentNullException  gt  lt  exception gt       lt exception cref  UriFormatException  gt  lt  exception gt       lt exception cref  InvalidOperationException  gt  lt  exception gt  public static String MakeRelativePath String fromPath  String toPath        if  String IsNullOrEmpty fromPath   throw new ArgumentNullException  fromPath        if  String IsNullOrEmpty toPath     throw new ArgumentNullException  toPath         Uri fromUri   new Uri fromPath       Uri toUri   new Uri toPath        if  fromUri Scheme    toUri Scheme    return toPath       path can t be made relative       Uri relativeUri   fromUri MakeRelativeUri toUri       String relativePath   Uri UnescapeDataString relativeUri ToString          if  toUri Scheme Equals  file   StringComparison InvariantCultureIgnoreCase                 relativePath   relativePath Replace Path AltDirectorySeparatorChar  Path DirectorySeparatorChar              return relativePath

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If you are using  NET Core 2 0  Path GetRelativePath   is available providing this specific functionality           var relativeTo     C  Program Files Dummy Folder MyProgram           var path     C  Program Files Dummy Folder MyProgram Data datafile1 dat            string relativePath   System IO Path GetRelativePath relativeTo  path            System Console WriteLine relativePath              output -- gt  Data datafile1 dat    Otherwise  for  NET full framework  as of v4 7  recommend using one of the other suggested answers

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You want to use the CommonPath method of this RelativePath class  Once you have the common path  just strip it out of the path you want to display   Namespace IO Path      Public NotInheritable Class RelativePath          Private Declare Function PathRelativePathTo Lib  shlwapi  Alias  PathRelativePathToA                  ByVal pszPath As String                ByVal pszFrom As String                ByVal dwAttrFrom As Integer                ByVal pszTo As String                ByVal dwAttrTo As Integer  As Integer          Private Declare Function PathCanonicalize Lib  shlwapi  Alias  PathCanonicalizeA                  ByVal pszBuf As String                ByVal pszPath As String  As Integer          Private Const FILE ATTRIBUTE DIRECTORY As Short    amp H10S          Private Const MAX PATH As Short   260          Private  path As String         Private  isDirectory As Boolean   Region   Constructors            Public Sub New            End Sub          Public Sub New ByVal path As String               path   path         End Sub          Public Sub New ByVal path As String  ByVal isDirectory As Boolean               path   path              isDirectory   isDirectory         End Sub   End Region          Private Shared Function StripNulls ByVal value As String  As String             StripNulls   value             If  InStr value  vbNullChar   gt  0  Then                 StripNulls   Left value  InStr value  vbNullChar  - 1              End If         End Function          Private Shared Function TrimCurrentDirectory ByVal path As String  As String             TrimCurrentDirectory   path             If Len path   gt   2 And Left path  2         Then                 TrimCurrentDirectory   Mid path  3              End If         End Function               lt summary gt              3  conforming to general principles  conforming to accepted principles or standard practice              lt  summary gt          Public Shared Function Canonicalize ByVal path As String  As String             Dim sPath As String              sPath   New String Chr 0   MAX PATH               If PathCanonicalize sPath  path    0 Then                 Canonicalize   vbNullString             Else                 Canonicalize   StripNulls sPath              End If          End Function               lt summary gt              Returns the most common path between two paths               lt  summary gt               lt remarks gt               lt para gt returns the path that is common between two paths lt  para gt               lt para gt c  FolderA FolderB FolderC lt  para gt                c  FolderA FolderD FolderE File Ext                            results in                    c  FolderA               lt  remarks gt          Public Shared Function CommonPath ByVal path1 As String  ByVal path2 As String  As String              returns the path that is common between two paths                               c  FolderA FolderB FolderC                 c  FolderA FolderD FolderE File Ext                               results in                      c  FolderA               Dim sResult As String   String Empty             Dim iPos1  iPos2 As Integer             path1   Canonicalize path1              path2   Canonicalize path2              Do                 If Left path1  iPos1    Left path2  iPos2  Then                     sResult   Left path1  iPos1                  End If                 iPos1   InStr iPos1   1  path1                       iPos2   InStr iPos2   1  path1                   Loop While Left path1  iPos1    Left path2  iPos2               Return sResult          End Function          Public Function CommonPath ByVal path As String  As String             Return CommonPath  path  path          End Function          Public Shared Function RelativePathTo ByVal source As String  ByVal isSourceDirectory As Boolean  ByVal target As String  ByVal isTargetDirectory As Boolean  As String              DEVLIB                 05 23 05  1 47PM - Fixed call to PathRelativePathTo  iTargetAttribute is now passed to dwAttrTo instead of IsTargetDirectory                      For Visual Basic 6 0  the fix does not change testing results                          because when the Boolean IsTargetDirectory is converted to the Long dwAttrTo it happens to contain FILE ATTRIBUTE DIRECTORY                            Dim sRelativePath As String             Dim iSourceAttribute  iTargetAttribute As Integer              sRelativePath   New String Chr 0   MAX PATH              source   Canonicalize source              target   Canonicalize target               If isSourceDirectory Then                 iSourceAttribute   FILE ATTRIBUTE DIRECTORY             End If              If isTargetDirectory Then                 iTargetAttribute   FILE ATTRIBUTE DIRECTORY             End If              If PathRelativePathTo sRelativePath  source  iSourceAttribute  target  iTargetAttribute    0 Then                 RelativePathTo   vbNullString             Else                 RelativePathTo   TrimCurrentDirectory StripNulls sRelativePath               End If          End Function          Public Function RelativePath ByVal target As String  As String             Return RelativePathTo  path   isDirectory  target  False          End Function      End Class  End Namespace

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If you know that toPath is contained by fromPath then you can keep it simple  I ll leave out the asserts for brevity   public static string MakeRelativePath string fromPath  string toPath           use Path GetFullPath to canonicalise the paths  deal with multiple directory seperators  etc      return Path GetFullPath toPath  Substring Path GetFullPath fromPath  Length   1

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If you have a readonly text box  could you not not make it a label and set AutoEllipsis true   alternatively there are posts with code for generating the autoellipsis yourself   this does it for a grid  you would need to pass i the width for the text box instead   It isn t quite right as it hacks off a bit more than is necessary  and I haven t got around to finding where the calculation is incorrect  it would be easy enough to modify to remove the first part of the directory rather than the last if you desire   Private Function AddEllipsisPath ByVal text As String  ByVal colIndex As Integer  ByVal grid As DataGridView  As String      Get the size with the column s width      Dim colWidth As Integer   grid Columns colIndex  Width       Calculate the dimensions of the text with the current font     Dim textSize As SizeF   MeasureString text  grid Font       Dim rawText As String   text     Dim FileNameLen As Integer   text Length - text LastIndexOf          Dim ReplaceWith As String               Do While textSize Width  gt  colWidth           Trim to make room for the ellipsis         Dim LastFolder As Integer   rawText LastIndexOf      rawText Length - FileNameLen - 1           If LastFolder  lt  0 Then             Exit Do         End If          rawText   rawText Substring 0  LastFolder    ReplaceWith   rawText Substring rawText Length - FileNameLen           If ReplaceWith Length  gt  0 Then             FileNameLen    4             ReplaceWith              End If         textSize   MeasureString rawText  grid Font      Loop      Return rawText End Function  Private Function MeasureString ByVal text As String  ByVal fontInfo As Font  As SizeF     Dim size As SizeF     Dim emSize As Single   fontInfo Size     If emSize   0 Then emSize   12      Dim stringFont As New Font fontInfo Name  emSize       Dim bmp As New Bitmap 1000  100      Dim g As Graphics   Graphics FromImage bmp       size   g MeasureString text  stringFont      g Dispose       Return size End Function

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NET Core 2 0 has Path GetRelativePath  else  use this        lt summary gt      Creates a relative path from one file or folder to another       lt  summary gt       lt param name  fromPath  gt Contains the directory that defines the start of the relative path  lt  param gt       lt param name  toPath  gt Contains the path that defines the endpoint of the relative path  lt  param gt       lt returns gt The relative path from the start directory to the end path or  lt c gt toPath lt  c gt  if the paths are not related  lt  returns gt       lt exception cref  ArgumentNullException  gt  lt  exception gt       lt exception cref  UriFormatException  gt  lt  exception gt       lt exception cref  InvalidOperationException  gt  lt  exception gt  public static String MakeRelativePath String fromPath  String toPath        if  String IsNullOrEmpty fromPath   throw new ArgumentNullException  fromPath        if  String IsNullOrEmpty toPath     throw new ArgumentNullException  toPath         Uri fromUri   new Uri fromPath       Uri toUri   new Uri toPath        if  fromUri Scheme    toUri Scheme    return toPath       path can t be made relative       Uri relativeUri   fromUri MakeRelativeUri toUri       String relativePath   Uri UnescapeDataString relativeUri ToString          if  toUri Scheme Equals  file   StringComparison InvariantCultureIgnoreCase                 relativePath   relativePath Replace Path AltDirectorySeparatorChar  Path DirectorySeparatorChar              return relativePath

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As Alex Brault points out  especially on Windows  the absolute path  with drive letter and all  is unambiguous and often better   Shouldn t your OpenFileDialog use a regular tree-browser structure   To get some nomenclature in place  the RefDir is the directory relative to which you want to specify the path  the AbsName is the absolute path name that you want to map  and the RelPath is the resulting relative path   Take the first of these options that matches    If you have different drive letters  there is no relative path from RefDir to AbsName  you must use the AbsName  If the AbsName is in a sub-directory of RefDir or is a file within RefDir then simply remove the RefDir from the start of AbsName to create RelPath  optionally prepend       or      since you are on Windows   Find the longest common prefix of RefDir and AbsName  where D  Abc Def and D  Abc Default share D  Abc as the longest common prefix  it has to be a mapping of name components  not a simple longest common substring   call it LCP   Remove LCP from AbsName and RefDir   For each path component left in  RefDir - LCP   prepend       to  AbsName - LCP  to yield RelPath    To illustrate the last rule  which is  of course  by far the most complex   start with   RefDir   D  Abc Def Ghi AbsName   D  Abc Default Karma Crucible   Then  LCP   D  Abc  RefDir - LCP    Def Ghi  Absname - LCP    Default Karma Crucible RelPath         Default Karma Crucible   While I was typing  DavidK produced an answer which suggests that you are not the first to need this feature and that there is a standard function to do this job   Use it   But there s no harm in being able to think your way through from first principles  either   Except that Unix systems do not support drive letters  so everything is always located under the same root directory  and the first bullet therefore is irrelevant   the same technique could be used on Unix

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Use   RelPath   AbsPath Replace ApplicationPath

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I have used this in the past        lt summary gt      Creates a relative path from one file     or folder to another       lt  summary gt       lt param name  fromDirectory  gt      Contains the directory that defines the     start of the relative path       lt  param gt       lt param name  toPath  gt      Contains the path that defines the     endpoint of the relative path       lt  param gt       lt returns gt      The relative path from the start     directory to the end path       lt  returns gt       lt exception cref  ArgumentNullException  gt  lt  exception gt  public static string MakeRelative string fromDirectory  string toPath      if  fromDirectory    null      throw new ArgumentNullException  fromDirectory       if  toPath    null      throw new ArgumentNullException  toPath       bool isRooted    Path IsPathRooted fromDirectory   amp  amp  Path IsPathRooted toPath       if  isRooted          bool isDifferentRoot    string Compare Path GetPathRoot fromDirectory   Path GetPathRoot toPath   true     0        if  isDifferentRoot        return toPath         List lt string gt  relativePath   new List lt string gt       string   fromDirectories   fromDirectory Split Path DirectorySeparatorChar      string   toDirectories   toPath Split Path DirectorySeparatorChar      int length   Math Min fromDirectories Length  toDirectories Length      int lastCommonRoot   -1        find common root   for  int x   0  x  lt  length  x            if  string Compare fromDirectories x   toDirectories x   true     0        break       lastCommonRoot   x         if  lastCommonRoot    -1      return toPath        add relative folders in from path   for  int x   lastCommonRoot   1  x  lt  fromDirectories Length  x            if  fromDirectories x  Length  gt  0        relativePath Add                  add to folders to path   for  int x   lastCommonRoot   1  x  lt  toDirectories Length  x            relativePath Add toDirectories x              create relative path   string   relativeParts   new string relativePath Count     relativePath CopyTo relativeParts  0      string newPath   string Join Path DirectorySeparatorChar ToString    relativeParts      return newPath

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There is a Win32  C    function in shlwapi dll that does exactly what you want  PathRelativePathTo    I m not aware of any way to access this from  NET other than to P Invoke it  though

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I d split both of your paths at the directory level  From there  find the point of divergence and work your way back to the assembly folder  prepending a       everytime you pass a directory   Keep in mind however  that an absolute path works everywhere and is usually easier to read than a relative one  I personally wouldn t show an user a relative path unless it was absolutely necessary

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The function that uses URI returned  almost  relative path  It included directory that directly contains the file which relative path I wanted to get   Some time ago I wrote a simple function that returns relative path of folder or file  and even if it s on another drive  it includes the drive letter as well   Please take a look       public static string GetRelativePath string BasePath  string AbsolutePath                char Separator   Path DirectorySeparatorChar          if  string IsNullOrWhiteSpace BasePath   BasePath   Directory GetCurrentDirectory            var ReturnPath               var CommonPart               var BasePathFolders   BasePath Split Separator           var AbsolutePathFolders   AbsolutePath Split Separator           var i   0          while  i  lt  BasePathFolders Length  amp  i  lt  AbsolutePathFolders Length                        if  BasePathFolders i  ToLower      AbsolutePathFolders i  ToLower                                  CommonPart    BasePathFolders i    Separator                            else                               break                            i    1                    if  CommonPart Length  gt  0                        var parents   BasePath Substring CommonPart Length - 1  Split Separator               foreach  var ParentDir in parents                                if   string IsNullOrEmpty ParentDir                       ReturnPath           Separator                                  ReturnPath    AbsolutePath Substring CommonPart Length           return ReturnPath

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NET Core 2 0 has Path GetRelativePath  else  use this        lt summary gt      Creates a relative path from one file or folder to another       lt  summary gt       lt param name  fromPath  gt Contains the directory that defines the start of the relative path  lt  param gt       lt param name  toPath  gt Contains the path that defines the endpoint of the relative path  lt  param gt       lt returns gt The relative path from the start directory to the end path or  lt c gt toPath lt  c gt  if the paths are not related  lt  returns gt       lt exception cref  ArgumentNullException  gt  lt  exception gt       lt exception cref  UriFormatException  gt  lt  exception gt       lt exception cref  InvalidOperationException  gt  lt  exception gt  public static String MakeRelativePath String fromPath  String toPath        if  String IsNullOrEmpty fromPath   throw new ArgumentNullException  fromPath        if  String IsNullOrEmpty toPath     throw new ArgumentNullException  toPath         Uri fromUri   new Uri fromPath       Uri toUri   new Uri toPath        if  fromUri Scheme    toUri Scheme    return toPath       path can t be made relative       Uri relativeUri   fromUri MakeRelativeUri toUri       String relativePath   Uri UnescapeDataString relativeUri ToString          if  toUri Scheme Equals  file   StringComparison InvariantCultureIgnoreCase                 relativePath   relativePath Replace Path AltDirectorySeparatorChar  Path DirectorySeparatorChar              return relativePath

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here s mine   public static string RelativePathTo this System IO DirectoryInfo  this  string to        var rgFrom    this FullName Split new     Path DirectorySeparatorChar  Path AltDirectorySeparatorChar    StringSplitOptions RemoveEmptyEntries       var rgTo   to Split new     Path DirectorySeparatorChar  Path AltDirectorySeparatorChar    StringSplitOptions RemoveEmptyEntries       var cSame   rgFrom TakeWhile  p  i    gt  i  lt  rgTo Length  amp  amp  string Equals p  rgTo i    Count         return Path Combine          Enumerable Range 0  rgFrom Length - cSame           Select     gt                 Concat rgTo Skip cSame            ToArray

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A bit late to the question  but I just needed this feature as well   I agree with DavidK that since there is a built-in API function that provides this  you should use it   Here s a managed wrapper for it   public static string GetRelativePath string fromPath  string toPath        int fromAttr   GetPathAttribute fromPath       int toAttr   GetPathAttribute toPath        StringBuilder path   new StringBuilder 260      MAX PATH     if PathRelativePathTo          path          fromPath          fromAttr          toPath          toAttr     0                throw new ArgumentException  Paths must have a common prefix              return path ToString       private static int GetPathAttribute string path        DirectoryInfo di   new DirectoryInfo path       if  di Exists                return FILE ATTRIBUTE DIRECTORY             FileInfo fi   new FileInfo path       if fi Exists                return FILE ATTRIBUTE NORMAL             throw new FileNotFoundException       private const int FILE ATTRIBUTE DIRECTORY   0x10  private const int FILE ATTRIBUTE NORMAL   0x80    DllImport  shlwapi dll   SetLastError   true   private static extern int PathRelativePathTo StringBuilder pszPath       string pszFrom  int dwAttrFrom  string pszTo  int dwAttrTo

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It s a long way around  but System Uri class has a method named MakeRelativeUri  Maybe you could use that  It s a shame really that System IO Path doesn t have this

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If you have a readonly text box  could you not not make it a label and set AutoEllipsis true   alternatively there are posts with code for generating the autoellipsis yourself   this does it for a grid  you would need to pass i the width for the text box instead   It isn t quite right as it hacks off a bit more than is necessary  and I haven t got around to finding where the calculation is incorrect  it would be easy enough to modify to remove the first part of the directory rather than the last if you desire   Private Function AddEllipsisPath ByVal text As String  ByVal colIndex As Integer  ByVal grid As DataGridView  As String      Get the size with the column s width      Dim colWidth As Integer   grid Columns colIndex  Width       Calculate the dimensions of the text with the current font     Dim textSize As SizeF   MeasureString text  grid Font       Dim rawText As String   text     Dim FileNameLen As Integer   text Length - text LastIndexOf          Dim ReplaceWith As String               Do While textSize Width  gt  colWidth           Trim to make room for the ellipsis         Dim LastFolder As Integer   rawText LastIndexOf      rawText Length - FileNameLen - 1           If LastFolder  lt  0 Then             Exit Do         End If          rawText   rawText Substring 0  LastFolder    ReplaceWith   rawText Substring rawText Length - FileNameLen           If ReplaceWith Length  gt  0 Then             FileNameLen    4             ReplaceWith              End If         textSize   MeasureString rawText  grid Font      Loop      Return rawText End Function  Private Function MeasureString ByVal text As String  ByVal fontInfo As Font  As SizeF     Dim size As SizeF     Dim emSize As Single   fontInfo Size     If emSize   0 Then emSize   12      Dim stringFont As New Font fontInfo Name  emSize       Dim bmp As New Bitmap 1000  100      Dim g As Graphics   Graphics FromImage bmp       size   g MeasureString text  stringFont      g Dispose       Return size End Function

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In ASP NET Core 2  if you want the relative path to bin Debug netcoreapp2 2 you can use the following combination    using Microsoft AspNetCore Hosting  using Microsoft Extensions Configuration  public class RenderingService   IRenderingService        private readonly IHostingEnvironment  hostingEnvironment      public RenderingService IHostingEnvironment hostingEnvironment             hostingEnvironment   hostingEnvironment             public string RelativeAssemblyDirectory                 var contentRootPath    hostingEnvironment ContentRootPath          string executingAssemblyDirectoryAbsolutePath   System IO Path GetDirectoryName System Reflection Assembly GetExecutingAssembly   Location           string executingAssemblyDirectoryRelativePath   System IO Path GetRelativePath contentRootPath  executingAssemblyDirectoryAbsolutePath           return executingAssemblyDirectoryRelativePath

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In ASP NET Core 2  if you want the relative path to bin Debug netcoreapp2 2 you can use the following combination    using Microsoft AspNetCore Hosting  using Microsoft Extensions Configuration  public class RenderingService   IRenderingService        private readonly IHostingEnvironment  hostingEnvironment      public RenderingService IHostingEnvironment hostingEnvironment             hostingEnvironment   hostingEnvironment             public string RelativeAssemblyDirectory                 var contentRootPath    hostingEnvironment ContentRootPath          string executingAssemblyDirectoryAbsolutePath   System IO Path GetDirectoryName System Reflection Assembly GetExecutingAssembly   Location           string executingAssemblyDirectoryRelativePath   System IO Path GetRelativePath contentRootPath  executingAssemblyDirectoryAbsolutePath           return executingAssemblyDirectoryRelativePath

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There is a Win32  C    function in shlwapi dll that does exactly what you want  PathRelativePathTo    I m not aware of any way to access this from  NET other than to P Invoke it  though

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There is a Win32  C    function in shlwapi dll that does exactly what you want  PathRelativePathTo    I m not aware of any way to access this from  NET other than to P Invoke it  though

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Use   RelPath   AbsPath Replace ApplicationPath

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public static string ToRelativePath string filePath  string refPath                var pathNormalized   Path GetFullPath filePath            var refNormalized   Path GetFullPath refPath           refNormalized   refNormalized TrimEnd                      if   pathNormalized StartsWith refNormalized               throw new ArgumentException            var res   pathNormalized Substring refNormalized Length   1           return res

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It s a long way around  but System Uri class has a method named MakeRelativeUri  Maybe you could use that  It s a shame really that System IO Path doesn t have this

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As Alex Brault points out  especially on Windows  the absolute path  with drive letter and all  is unambiguous and often better   Shouldn t your OpenFileDialog use a regular tree-browser structure   To get some nomenclature in place  the RefDir is the directory relative to which you want to specify the path  the AbsName is the absolute path name that you want to map  and the RelPath is the resulting relative path   Take the first of these options that matches    If you have different drive letters  there is no relative path from RefDir to AbsName  you must use the AbsName  If the AbsName is in a sub-directory of RefDir or is a file within RefDir then simply remove the RefDir from the start of AbsName to create RelPath  optionally prepend       or      since you are on Windows   Find the longest common prefix of RefDir and AbsName  where D  Abc Def and D  Abc Default share D  Abc as the longest common prefix  it has to be a mapping of name components  not a simple longest common substring   call it LCP   Remove LCP from AbsName and RefDir   For each path component left in  RefDir - LCP   prepend       to  AbsName - LCP  to yield RelPath    To illustrate the last rule  which is  of course  by far the most complex   start with   RefDir   D  Abc Def Ghi AbsName   D  Abc Default Karma Crucible   Then  LCP   D  Abc  RefDir - LCP    Def Ghi  Absname - LCP    Default Karma Crucible RelPath         Default Karma Crucible   While I was typing  DavidK produced an answer which suggests that you are not the first to need this feature and that there is a standard function to do this job   Use it   But there s no harm in being able to think your way through from first principles  either   Except that Unix systems do not support drive letters  so everything is always located under the same root directory  and the first bullet therefore is irrelevant   the same technique could be used on Unix

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The function that uses URI returned  almost  relative path  It included directory that directly contains the file which relative path I wanted to get   Some time ago I wrote a simple function that returns relative path of folder or file  and even if it s on another drive  it includes the drive letter as well   Please take a look       public static string GetRelativePath string BasePath  string AbsolutePath                char Separator   Path DirectorySeparatorChar          if  string IsNullOrWhiteSpace BasePath   BasePath   Directory GetCurrentDirectory            var ReturnPath               var CommonPart               var BasePathFolders   BasePath Split Separator           var AbsolutePathFolders   AbsolutePath Split Separator           var i   0          while  i  lt  BasePathFolders Length  amp  i  lt  AbsolutePathFolders Length                        if  BasePathFolders i  ToLower      AbsolutePathFolders i  ToLower                                  CommonPart    BasePathFolders i    Separator                            else                               break                            i    1                    if  CommonPart Length  gt  0                        var parents   BasePath Substring CommonPart Length - 1  Split Separator               foreach  var ParentDir in parents                                if   string IsNullOrEmpty ParentDir                       ReturnPath           Separator                                  ReturnPath    AbsolutePath Substring CommonPart Length           return ReturnPath

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You want to use the CommonPath method of this RelativePath class  Once you have the common path  just strip it out of the path you want to display   Namespace IO Path      Public NotInheritable Class RelativePath          Private Declare Function PathRelativePathTo Lib  shlwapi  Alias  PathRelativePathToA                  ByVal pszPath As String                ByVal pszFrom As String                ByVal dwAttrFrom As Integer                ByVal pszTo As String                ByVal dwAttrTo As Integer  As Integer          Private Declare Function PathCanonicalize Lib  shlwapi  Alias  PathCanonicalizeA                  ByVal pszBuf As String                ByVal pszPath As String  As Integer          Private Const FILE ATTRIBUTE DIRECTORY As Short    amp H10S          Private Const MAX PATH As Short   260          Private  path As String         Private  isDirectory As Boolean   Region   Constructors            Public Sub New            End Sub          Public Sub New ByVal path As String               path   path         End Sub          Public Sub New ByVal path As String  ByVal isDirectory As Boolean               path   path              isDirectory   isDirectory         End Sub   End Region          Private Shared Function StripNulls ByVal value As String  As String             StripNulls   value             If  InStr value  vbNullChar   gt  0  Then                 StripNulls   Left value  InStr value  vbNullChar  - 1              End If         End Function          Private Shared Function TrimCurrentDirectory ByVal path As String  As String             TrimCurrentDirectory   path             If Len path   gt   2 And Left path  2         Then                 TrimCurrentDirectory   Mid path  3              End If         End Function               lt summary gt              3  conforming to general principles  conforming to accepted principles or standard practice              lt  summary gt          Public Shared Function Canonicalize ByVal path As String  As String             Dim sPath As String              sPath   New String Chr 0   MAX PATH               If PathCanonicalize sPath  path    0 Then                 Canonicalize   vbNullString             Else                 Canonicalize   StripNulls sPath              End If          End Function               lt summary gt              Returns the most common path between two paths               lt  summary gt               lt remarks gt               lt para gt returns the path that is common between two paths lt  para gt               lt para gt c  FolderA FolderB FolderC lt  para gt                c  FolderA FolderD FolderE File Ext                            results in                    c  FolderA               lt  remarks gt          Public Shared Function CommonPath ByVal path1 As String  ByVal path2 As String  As String              returns the path that is common between two paths                               c  FolderA FolderB FolderC                 c  FolderA FolderD FolderE File Ext                               results in                      c  FolderA               Dim sResult As String   String Empty             Dim iPos1  iPos2 As Integer             path1   Canonicalize path1              path2   Canonicalize path2              Do                 If Left path1  iPos1    Left path2  iPos2  Then                     sResult   Left path1  iPos1                  End If                 iPos1   InStr iPos1   1  path1                       iPos2   InStr iPos2   1  path1                   Loop While Left path1  iPos1    Left path2  iPos2               Return sResult          End Function          Public Function CommonPath ByVal path As String  As String             Return CommonPath  path  path          End Function          Public Shared Function RelativePathTo ByVal source As String  ByVal isSourceDirectory As Boolean  ByVal target As String  ByVal isTargetDirectory As Boolean  As String              DEVLIB                 05 23 05  1 47PM - Fixed call to PathRelativePathTo  iTargetAttribute is now passed to dwAttrTo instead of IsTargetDirectory                      For Visual Basic 6 0  the fix does not change testing results                          because when the Boolean IsTargetDirectory is converted to the Long dwAttrTo it happens to contain FILE ATTRIBUTE DIRECTORY                            Dim sRelativePath As String             Dim iSourceAttribute  iTargetAttribute As Integer              sRelativePath   New String Chr 0   MAX PATH              source   Canonicalize source              target   Canonicalize target               If isSourceDirectory Then                 iSourceAttribute   FILE ATTRIBUTE DIRECTORY             End If              If isTargetDirectory Then                 iTargetAttribute   FILE ATTRIBUTE DIRECTORY             End If              If PathRelativePathTo sRelativePath  source  iSourceAttribute  target  iTargetAttribute    0 Then                 RelativePathTo   vbNullString             Else                 RelativePathTo   TrimCurrentDirectory StripNulls sRelativePath               End If          End Function          Public Function RelativePath ByVal target As String  As String             Return RelativePathTo  path   isDirectory  target  False          End Function      End Class  End Namespace

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I have used this in the past        lt summary gt      Creates a relative path from one file     or folder to another       lt  summary gt       lt param name  fromDirectory  gt      Contains the directory that defines the     start of the relative path       lt  param gt       lt param name  toPath  gt      Contains the path that defines the     endpoint of the relative path       lt  param gt       lt returns gt      The relative path from the start     directory to the end path       lt  returns gt       lt exception cref  ArgumentNullException  gt  lt  exception gt  public static string MakeRelative string fromDirectory  string toPath      if  fromDirectory    null      throw new ArgumentNullException  fromDirectory       if  toPath    null      throw new ArgumentNullException  toPath       bool isRooted    Path IsPathRooted fromDirectory   amp  amp  Path IsPathRooted toPath       if  isRooted          bool isDifferentRoot    string Compare Path GetPathRoot fromDirectory   Path GetPathRoot toPath   true     0        if  isDifferentRoot        return toPath         List lt string gt  relativePath   new List lt string gt       string   fromDirectories   fromDirectory Split Path DirectorySeparatorChar      string   toDirectories   toPath Split Path DirectorySeparatorChar      int length   Math Min fromDirectories Length  toDirectories Length      int lastCommonRoot   -1        find common root   for  int x   0  x  lt  length  x            if  string Compare fromDirectories x   toDirectories x   true     0        break       lastCommonRoot   x         if  lastCommonRoot    -1      return toPath        add relative folders in from path   for  int x   lastCommonRoot   1  x  lt  fromDirectories Length  x            if  fromDirectories x  Length  gt  0        relativePath Add                  add to folders to path   for  int x   lastCommonRoot   1  x  lt  toDirectories Length  x            relativePath Add toDirectories x              create relative path   string   relativeParts   new string relativePath Count     relativePath CopyTo relativeParts  0      string newPath   string Join Path DirectorySeparatorChar ToString    relativeParts      return newPath

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NET Core 2 0 Answer   NET Core 2 0 has Path GetRelativePath which can be used like so   var relativePath   Path GetRelativePath        C  Program Files Dummy Folder MyProgram         C  Program Files Dummy Folder MyProgram Data datafile1 dat      In the above example  the relativePath variable is equal to Data datafile1 dat   Alternative  NET Answer   Dave s solution does not work when the file paths do not end with a forward slash character     which can happen if the path is a directory path  My solution fixes that problem and also makes use of the Uri UriSchemeFile constant instead of hard coding  FILE         lt summary gt      Creates a relative path from one file or folder to another       lt  summary gt       lt param name  fromPath  gt Contains the directory that defines the start of the relative path  lt  param gt       lt param name  toPath  gt Contains the path that defines the endpoint of the relative path  lt  param gt       lt returns gt The relative path from the start directory to the end path  lt  returns gt       lt exception cref  ArgumentNullException  gt  lt paramref name  fromPath   gt  or  lt paramref name  toPath   gt  is  lt c gt null lt  c gt   lt  exception gt       lt exception cref  UriFormatException  gt  lt  exception gt       lt exception cref  InvalidOperationException  gt  lt  exception gt  public static string GetRelativePath string fromPath  string toPath        if  string IsNullOrEmpty fromPath                 throw new ArgumentNullException  fromPath               if  string IsNullOrEmpty toPath                 throw new ArgumentNullException  toPath               Uri fromUri   new Uri AppendDirectorySeparatorChar fromPath        Uri toUri   new Uri AppendDirectorySeparatorChar toPath         if  fromUri Scheme    toUri Scheme                return toPath             Uri relativeUri   fromUri MakeRelativeUri toUri       string relativePath   Uri UnescapeDataString relativeUri ToString          if  string Equals toUri Scheme  Uri UriSchemeFile  StringComparison OrdinalIgnoreCase                 relativePath   relativePath Replace Path AltDirectorySeparatorChar  Path DirectorySeparatorChar              return relativePath     private static string AppendDirectorySeparatorChar string path           Append a slash only if the path is a directory and does not have a slash      if   Path HasExtension path   amp  amp           path EndsWith Path DirectorySeparatorChar ToString                   return path   Path DirectorySeparatorChar             return path      Windows Interop Answer  There is a Windows API called PathRelativePathToA that can be used to find a relative path  Please note that the file or directory paths that you pass to the function must exist for it to work   var relativePath   PathExtended GetRelativePath        C  Program Files Dummy Folder MyProgram         C  Program Files Dummy Folder MyProgram Data datafile1 dat     public static class PathExtended       private const int FILE ATTRIBUTE DIRECTORY   0x10      private const int FILE ATTRIBUTE NORMAL   0x80      private const int MaximumPath   260       public static string GetRelativePath string fromPath  string toPath                var fromAttribute   GetPathAttribute fromPath           var toAttribute   GetPathAttribute toPath            var stringBuilder   new StringBuilder MaximumPath           if  PathRelativePathTo              stringBuilder              fromPath              fromAttribute              toPath              toAttribute     0                        throw new ArgumentException  Paths must have a common prefix                        return stringBuilder ToString               private static int GetPathAttribute string path                var directory   new DirectoryInfo path           if  directory Exists                        return FILE ATTRIBUTE DIRECTORY                     var file   new FileInfo path           if  file Exists                        return FILE ATTRIBUTE NORMAL                     throw new FileNotFoundException               A file or directory with the specified path was not found                path               DllImport  shlwapi dll   SetLastError   true       private static extern int PathRelativePathTo          StringBuilder pszPath          string pszFrom          int dwAttrFrom          string pszTo          int dwAttrTo

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As pointed above  NET Core 2 x has implementation of Path GetRelativePath    Code below is adapted from sources and works fine with  NET 4 7 1 Framework      Licensed to the  NET Foundation under one or more agreements     The  NET Foundation licenses this file to you under the MIT license     See the LICENSE file in the project root for more information     Adapted from https   github com dotnet corefx blob master src Common src CoreLib System IO Path cs L697    by Anton Krouglov  using System Runtime CompilerServices  using System Diagnostics  using System Text  using Xunit   namespace System IO          Provides methods for processing file system strings in a cross-platform manner         Most of the methods don t do a complete parsing  such as examining a UNC hostname           but they will handle most string operations      public static class PathNetCore                 lt summary gt              Create a relative path from one path to another  Paths will be resolved before calculating the difference              Default path comparison for the active platform will be used  OrdinalIgnoreCase for Windows or Mac  Ordinal for Unix                lt  summary gt               lt param name  relativeTo  gt The source path the output should be relative to  This path is always considered to be a directory  lt  param gt               lt param name  path  gt The destination path  lt  param gt               lt returns gt The relative path or  lt paramref name  path   gt  if the paths don t share the same root  lt  returns gt               lt exception cref  ArgumentNullException  gt Thrown if  lt paramref name  relativeTo   gt  or  lt paramref name  path   gt  is  lt c gt null lt  c gt  or an empty string  lt  exception gt          public static string GetRelativePath string relativeTo  string path                return GetRelativePath relativeTo  path  StringComparison                      private static string GetRelativePath string relativeTo  string path  StringComparison comparisonType                if  string IsNullOrEmpty relativeTo   throw new ArgumentNullException nameof relativeTo                if  string IsNullOrEmpty path   throw new ArgumentNullException nameof path                Debug Assert comparisonType    StringComparison Ordinal                             comparisonType    StringComparison OrdinalIgnoreCase                relativeTo   Path GetFullPath relativeTo               path   Path GetFullPath path                   Need to check if the roots are different- if they are we need to return the  to  path              if   PathInternalNetCore AreRootsEqual relativeTo  path  comparisonType                   return path               int commonLength   PathInternalNetCore GetCommonPathLength relativeTo  path                  ignoreCase  comparisonType    StringComparison OrdinalIgnoreCase                   If there is nothing in common they can t share the same root  return the  to  path as is              if  commonLength    0                  return path                  Trailing separators aren t significant for comparison             int relativeToLength   relativeTo Length              if  PathInternalNetCore EndsInDirectorySeparator relativeTo                   relativeToLength--               bool pathEndsInSeparator   PathInternalNetCore EndsInDirectorySeparator path               int pathLength   path Length              if  pathEndsInSeparator                  pathLength--                  If we have effectively the same path  return                 if  relativeToLength    pathLength  amp  amp  commonLength  gt   relativeToLength  return                      We have the same root  we need to calculate the difference now using the                common Length and Segment count past the length                                Some examples                                 C  Foo C  Bar L3  S1 - gt     Bar                 C  Foo C  Foo Bar L6  S0 - gt  Bar                 C  Foo Bar C  Bar Bar L3  S2 - gt        Bar Bar                 C  Foo Foo C  Foo Bar L7  S1 - gt     Bar              StringBuilder                 sb   new StringBuilder      StringBuilderCache Acquire Math Max relativeTo Length  path Length                    Add parent segments for segments past the common on the  from  path             if  commonLength  lt  relativeToLength                    sb Append                         for  int i   commonLength   1  i  lt  relativeToLength  i                          if  PathInternalNetCore IsDirectorySeparator relativeTo i                              sb Append DirectorySeparatorChar                           sb Append                                                                          else if  PathInternalNetCore IsDirectorySeparator path commonLength                         No parent segments and we need to eat the initial separator                      C  Foo C  Foo Bar case                  commonLength                                  Now add the rest of the  to  path  adding back the trailing separator             int differenceLength   pathLength - commonLength              if  pathEndsInSeparator                  differenceLength                 if  differenceLength  gt  0                    if  sb Length  gt  0                        sb Append DirectorySeparatorChar                                      sb Append path  commonLength  differenceLength                              return sb ToString      StringBuilderCache GetStringAndRelease sb                         Public static readonly variant of the separators  The Path implementation itself is using            internal const variant of the separators for better performance          public static readonly char DirectorySeparatorChar   PathInternalNetCore DirectorySeparatorChar          public static readonly char AltDirectorySeparatorChar   PathInternalNetCore AltDirectorySeparatorChar          public static readonly char VolumeSeparatorChar   PathInternalNetCore VolumeSeparatorChar          public static readonly char PathSeparator   PathInternalNetCore PathSeparator                lt summary gt Returns a comparison that can be used to compare file and directory names for equality  lt  summary gt          internal static StringComparison StringComparison   gt  StringComparison OrdinalIgnoreCase                  lt summary gt Contains internal path helpers that are shared between many projects  lt  summary gt      internal static class PathInternalNetCore           internal const char DirectorySeparatorChar                 internal const char AltDirectorySeparatorChar                internal const char VolumeSeparatorChar                internal const char PathSeparator                 internal const string ExtendedDevicePathPrefix                    internal const string UncPathPrefix                  internal const string UncDevicePrefixToInsert       UNC            internal const string UncExtendedPathPrefix         UNC            internal const string DevicePathPrefix                       internal const int MaxShortPath   260                                       internal const int DevicePrefixLength   4                lt summary gt              Returns true if the two paths have the same root              lt  summary gt          internal static bool AreRootsEqual string first  string second  StringComparison comparisonType                int firstRootLength   GetRootLength first               int secondRootLength   GetRootLength second                return firstRootLength    secondRootLength                     amp  amp  string Compare                         strA  first                         indexA  0                         strB  second                         indexB  0                         length  firstRootLength                         comparisonType  comparisonType     0                          lt summary gt              Gets the length of the root of the path  drive  share  etc                 lt  summary gt          internal static int GetRootLength string path                int i   0              int volumeSeparatorLength   2     Length to the colon  C               int uncRootLength   2     Length to the start of the server name                   bool extendedSyntax   path StartsWith ExtendedDevicePathPrefix               bool extendedUncSyntax   path StartsWith UncExtendedPathPrefix               if  extendedSyntax                       Shift the position we look for the root from to account for the extended prefix                 if  extendedUncSyntax                                - gt       UNC                       uncRootLength   UncExtendedPathPrefix Length                                    else                           C   - gt       C                       volumeSeparatorLength    ExtendedDevicePathPrefix Length                                               if    extendedSyntax    extendedUncSyntax   amp  amp  path Length  gt  0  amp  amp  IsDirectorySeparator path 0                         UNC or simple rooted path  e g    foo   NOT      C  foo                    i   1      Drive rooted   foo  is one character                 if  extendedUncSyntax     path Length  gt  1  amp  amp  IsDirectorySeparator path 1                              UNC      UNC  or      scan past the next two directory separators at most                         e g  to     UNC Server Share or   Server Share                       i   uncRootLength                      int n   2     Maximum separators to skip                     while  i  lt  path Length  amp  amp    IsDirectorySeparator path i      --n  gt  0   i                                                else if  path Length  gt   volumeSeparatorLength  amp  amp                       path volumeSeparatorLength - 1     PathNetCore VolumeSeparatorChar                       Path is at least longer than where we expect a colon  and has a colon      A   A                      If the colon is followed by a directory separator  move past it                 i   volumeSeparatorLength                  if  path Length  gt   volumeSeparatorLength   1  amp  amp  IsDirectorySeparator path volumeSeparatorLength    i                               return i                          lt summary gt              True if the given character is a directory separator               lt  summary gt           MethodImpl MethodImplOptions AggressiveInlining           internal static bool IsDirectorySeparator char c                return c    PathNetCore DirectorySeparatorChar    c    PathNetCore AltDirectorySeparatorChar                          lt summary gt              Get the common path length from the start of the string               lt  summary gt          internal static int GetCommonPathLength string first  string second  bool ignoreCase                int commonChars   EqualStartingCharacterCount first  second  ignoreCase  ignoreCase                   If nothing matches             if  commonChars    0                  return commonChars                  Or we re a full string and equal length or match to a separator             if  commonChars    first Length                  amp  amp   commonChars    second Length    IsDirectorySeparator second commonChars                     return commonChars               if  commonChars    second Length  amp  amp  IsDirectorySeparator first commonChars                    return commonChars                  It s possible we matched somewhere in the middle of a segment e g  C  Foodie and C  Foobar              while  commonChars  gt  0  amp  amp   IsDirectorySeparator first commonChars - 1                    commonChars--               return commonChars                          lt summary gt              Gets the count of common characters from the left optionally ignoring case              lt  summary gt          internal static unsafe int EqualStartingCharacterCount string first  string second  bool ignoreCase                if  string IsNullOrEmpty first     string IsNullOrEmpty second   return 0               int commonChars   0               fixed  char  f   first              fixed  char  s   second                    char  l   f                  char  r   s                  char  leftEnd   l   first Length                  char  rightEnd   r   second Length                   while  l    leftEnd  amp  amp  r    rightEnd                                      amp  amp    l     r     ignoreCase  amp  amp                                                       char ToUpperInvariant   l      char ToUpperInvariant   r                            commonChars                        l                        r                                                 return commonChars                          lt summary gt              Returns true if the path ends in a directory separator               lt  summary gt          internal static bool EndsInDirectorySeparator string path                gt  path Length  gt  0  amp  amp  IsDirectorySeparator path path Length - 1                    lt summary gt  Tests for PathNetCore GetRelativePath  lt  summary gt      public static class GetRelativePathTests            Theory           InlineData   C       C                     InlineData   C  a     C  a                    InlineData   C  A     C  a                    InlineData   C  a      C  a                   InlineData   C       C  b     b             InlineData   C  a     C  b        b             InlineData   C  a     C  b         b              InlineData   C  a b     C  a                    InlineData   C  a b     C  a                     InlineData   C  a b      C  a                    InlineData   C  a b      C  a                     InlineData   C  a b c     C  a b                    InlineData   C  a b c     C  a b                     InlineData   C  a b c     C  a                       InlineData   C  a b c     C  a                        InlineData   C  a b c      C  a b                    InlineData   C  a b c      C  a b                     InlineData   C  a b c      C  a                       InlineData   C  a b c      C  a                        InlineData   C  a      C  b        b             InlineData   C  a     C  a b     b             InlineData   C  a     C  A b     b             InlineData   C  a     C  b c        b c             InlineData   C  a      C  a b     b             InlineData   C       D       D               InlineData   C       D  b     D  b             InlineData   C       D  b      D  b              InlineData   C  a     D  b     D  b             InlineData   C  a      D  b     D  b             InlineData   C  ab     C  a        a             InlineData   C  a     C  ab        ab             InlineData   C         LOCALHOST Share b       LOCALHOST Share b             InlineData     LOCALHOST Share a       LOCALHOST Share b        b               PlatformSpecific TestPlatforms Windows       Tests Windows-specific paths         public static void GetRelativePath Windows string relativeTo  string path  string expected                string result   PathNetCore GetRelativePath relativeTo  path               Assert Equal expected  result                   Check that we get the equivalent path when the result is combined with the sources             Assert Equal                  Path GetFullPath path  TrimEnd Path DirectorySeparatorChar                   Path GetFullPath Path Combine Path GetFullPath relativeTo   result                        TrimEnd Path DirectorySeparatorChar                   ignoreCase  true                  ignoreLineEndingDifferences  false                  ignoreWhiteSpaceDifferences  false

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A bit late to the question  but I just needed this feature as well   I agree with DavidK that since there is a built-in API function that provides this  you should use it   Here s a managed wrapper for it   public static string GetRelativePath string fromPath  string toPath        int fromAttr   GetPathAttribute fromPath       int toAttr   GetPathAttribute toPath        StringBuilder path   new StringBuilder 260      MAX PATH     if PathRelativePathTo          path          fromPath          fromAttr          toPath          toAttr     0                throw new ArgumentException  Paths must have a common prefix              return path ToString       private static int GetPathAttribute string path        DirectoryInfo di   new DirectoryInfo path       if  di Exists                return FILE ATTRIBUTE DIRECTORY             FileInfo fi   new FileInfo path       if fi Exists                return FILE ATTRIBUTE NORMAL             throw new FileNotFoundException       private const int FILE ATTRIBUTE DIRECTORY   0x10  private const int FILE ATTRIBUTE NORMAL   0x80    DllImport  shlwapi dll   SetLastError   true   private static extern int PathRelativePathTo StringBuilder pszPath       string pszFrom  int dwAttrFrom  string pszTo  int dwAttrTo

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There is a Win32  C    function in shlwapi dll that does exactly what you want  PathRelativePathTo    I m not aware of any way to access this from  NET other than to P Invoke it  though

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It s a long way around  but System Uri class has a method named MakeRelativeUri  Maybe you could use that  It s a shame really that System IO Path doesn t have this

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I d split both of your paths at the directory level  From there  find the point of divergence and work your way back to the assembly folder  prepending a       everytime you pass a directory   Keep in mind however  that an absolute path works everywhere and is usually easier to read than a relative one  I personally wouldn t show an user a relative path unless it was absolutely necessary

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I m using this   public static class StringExtensions          lt summary gt        Creates a relative path from one file or folder to another         lt  summary gt         lt param name  absPath  gt Absolute path  lt  param gt         lt param name  relTo  gt Directory that defines the start of the relative path  lt  param gt          lt returns gt The relative path from the start directory to the end path  lt  returns gt    public static string MakeRelativePath this string absPath  string relTo            string   absParts   absPath Split Path DirectorySeparatorChar         string   relParts   relTo Split Path DirectorySeparatorChar             Get the shortest of the two paths       int len   absParts Length  lt  relParts Length             absParts Length   relParts Length            Use to determine where in the loop we exited       int lastCommonRoot   -1        int index            Find common root       for  index   0  index  lt  len  index                      if  absParts index  Equals relParts index   StringComparison OrdinalIgnoreCase                 lastCommonRoot   index            else              break                    If we didn t find a common prefix then throw       if  lastCommonRoot    -1            throw new ArgumentException  The path of the two files doesn t have any common base               Build up the relative path       var relativePath   new StringBuilder              Add on the          for  index   lastCommonRoot   1  index  lt  relParts Length  index                    relativePath Append                relativePath Append Path DirectorySeparatorChar                     Add on the folders       for  index   lastCommonRoot   1  index  lt  absParts Length - 1  index                    relativePath Append absParts index            relativePath Append Path DirectorySeparatorChar                 relativePath Append absParts absParts Length - 1           return relativePath ToString

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I d split both of your paths at the directory level  From there  find the point of divergence and work your way back to the assembly folder  prepending a       everytime you pass a directory   Keep in mind however  that an absolute path works everywhere and is usually easier to read than a relative one  I personally wouldn t show an user a relative path unless it was absolutely necessary

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NET Core 2 0 Answer   NET Core 2 0 has Path GetRelativePath which can be used like so   var relativePath   Path GetRelativePath        C  Program Files Dummy Folder MyProgram         C  Program Files Dummy Folder MyProgram Data datafile1 dat      In the above example  the relativePath variable is equal to Data datafile1 dat   Alternative  NET Answer   Dave s solution does not work when the file paths do not end with a forward slash character     which can happen if the path is a directory path  My solution fixes that problem and also makes use of the Uri UriSchemeFile constant instead of hard coding  FILE         lt summary gt      Creates a relative path from one file or folder to another       lt  summary gt       lt param name  fromPath  gt Contains the directory that defines the start of the relative path  lt  param gt       lt param name  toPath  gt Contains the path that defines the endpoint of the relative path  lt  param gt       lt returns gt The relative path from the start directory to the end path  lt  returns gt       lt exception cref  ArgumentNullException  gt  lt paramref name  fromPath   gt  or  lt paramref name  toPath   gt  is  lt c gt null lt  c gt   lt  exception gt       lt exception cref  UriFormatException  gt  lt  exception gt       lt exception cref  InvalidOperationException  gt  lt  exception gt  public static string GetRelativePath string fromPath  string toPath        if  string IsNullOrEmpty fromPath                 throw new ArgumentNullException  fromPath               if  string IsNullOrEmpty toPath                 throw new ArgumentNullException  toPath               Uri fromUri   new Uri AppendDirectorySeparatorChar fromPath        Uri toUri   new Uri AppendDirectorySeparatorChar toPath         if  fromUri Scheme    toUri Scheme                return toPath             Uri relativeUri   fromUri MakeRelativeUri toUri       string relativePath   Uri UnescapeDataString relativeUri ToString          if  string Equals toUri Scheme  Uri UriSchemeFile  StringComparison OrdinalIgnoreCase                 relativePath   relativePath Replace Path AltDirectorySeparatorChar  Path DirectorySeparatorChar              return relativePath     private static string AppendDirectorySeparatorChar string path           Append a slash only if the path is a directory and does not have a slash      if   Path HasExtension path   amp  amp           path EndsWith Path DirectorySeparatorChar ToString                   return path   Path DirectorySeparatorChar             return path      Windows Interop Answer  There is a Windows API called PathRelativePathToA that can be used to find a relative path  Please note that the file or directory paths that you pass to the function must exist for it to work   var relativePath   PathExtended GetRelativePath        C  Program Files Dummy Folder MyProgram         C  Program Files Dummy Folder MyProgram Data datafile1 dat     public static class PathExtended       private const int FILE ATTRIBUTE DIRECTORY   0x10      private const int FILE ATTRIBUTE NORMAL   0x80      private const int MaximumPath   260       public static string GetRelativePath string fromPath  string toPath                var fromAttribute   GetPathAttribute fromPath           var toAttribute   GetPathAttribute toPath            var stringBuilder   new StringBuilder MaximumPath           if  PathRelativePathTo              stringBuilder              fromPath              fromAttribute              toPath              toAttribute     0                        throw new ArgumentException  Paths must have a common prefix                        return stringBuilder ToString               private static int GetPathAttribute string path                var directory   new DirectoryInfo path           if  directory Exists                        return FILE ATTRIBUTE DIRECTORY                     var file   new FileInfo path           if  file Exists                        return FILE ATTRIBUTE NORMAL                     throw new FileNotFoundException               A file or directory with the specified path was not found                path               DllImport  shlwapi dll   SetLastError   true       private static extern int PathRelativePathTo          StringBuilder pszPath          string pszFrom          int dwAttrFrom          string pszTo          int dwAttrTo

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I have used this in the past        lt summary gt      Creates a relative path from one file     or folder to another       lt  summary gt       lt param name  fromDirectory  gt      Contains the directory that defines the     start of the relative path       lt  param gt       lt param name  toPath  gt      Contains the path that defines the     endpoint of the relative path       lt  param gt       lt returns gt      The relative path from the start     directory to the end path       lt  returns gt       lt exception cref  ArgumentNullException  gt  lt  exception gt  public static string MakeRelative string fromDirectory  string toPath      if  fromDirectory    null      throw new ArgumentNullException  fromDirectory       if  toPath    null      throw new ArgumentNullException  toPath       bool isRooted    Path IsPathRooted fromDirectory   amp  amp  Path IsPathRooted toPath       if  isRooted          bool isDifferentRoot    string Compare Path GetPathRoot fromDirectory   Path GetPathRoot toPath   true     0        if  isDifferentRoot        return toPath         List lt string gt  relativePath   new List lt string gt       string   fromDirectories   fromDirectory Split Path DirectorySeparatorChar      string   toDirectories   toPath Split Path DirectorySeparatorChar      int length   Math Min fromDirectories Length  toDirectories Length      int lastCommonRoot   -1        find common root   for  int x   0  x  lt  length  x            if  string Compare fromDirectories x   toDirectories x   true     0        break       lastCommonRoot   x         if  lastCommonRoot    -1      return toPath        add relative folders in from path   for  int x   lastCommonRoot   1  x  lt  fromDirectories Length  x            if  fromDirectories x  Length  gt  0        relativePath Add                  add to folders to path   for  int x   lastCommonRoot   1  x  lt  toDirectories Length  x            relativePath Add toDirectories x              create relative path   string   relativeParts   new string relativePath Count     relativePath CopyTo relativeParts  0      string newPath   string Join Path DirectorySeparatorChar ToString    relativeParts      return newPath

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A bit late to the question  but I just needed this feature as well   I agree with DavidK that since there is a built-in API function that provides this  you should use it   Here s a managed wrapper for it   public static string GetRelativePath string fromPath  string toPath        int fromAttr   GetPathAttribute fromPath       int toAttr   GetPathAttribute toPath        StringBuilder path   new StringBuilder 260      MAX PATH     if PathRelativePathTo          path          fromPath          fromAttr          toPath          toAttr     0                throw new ArgumentException  Paths must have a common prefix              return path ToString       private static int GetPathAttribute string path        DirectoryInfo di   new DirectoryInfo path       if  di Exists                return FILE ATTRIBUTE DIRECTORY             FileInfo fi   new FileInfo path       if fi Exists                return FILE ATTRIBUTE NORMAL             throw new FileNotFoundException       private const int FILE ATTRIBUTE DIRECTORY   0x10  private const int FILE ATTRIBUTE NORMAL   0x80    DllImport  shlwapi dll   SetLastError   true   private static extern int PathRelativePathTo StringBuilder pszPath       string pszFrom  int dwAttrFrom  string pszTo  int dwAttrTo

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If you have a readonly text box  could you not not make it a label and set AutoEllipsis true   alternatively there are posts with code for generating the autoellipsis yourself   this does it for a grid  you would need to pass i the width for the text box instead   It isn t quite right as it hacks off a bit more than is necessary  and I haven t got around to finding where the calculation is incorrect  it would be easy enough to modify to remove the first part of the directory rather than the last if you desire   Private Function AddEllipsisPath ByVal text As String  ByVal colIndex As Integer  ByVal grid As DataGridView  As String      Get the size with the column s width      Dim colWidth As Integer   grid Columns colIndex  Width       Calculate the dimensions of the text with the current font     Dim textSize As SizeF   MeasureString text  grid Font       Dim rawText As String   text     Dim FileNameLen As Integer   text Length - text LastIndexOf          Dim ReplaceWith As String               Do While textSize Width  gt  colWidth           Trim to make room for the ellipsis         Dim LastFolder As Integer   rawText LastIndexOf      rawText Length - FileNameLen - 1           If LastFolder  lt  0 Then             Exit Do         End If          rawText   rawText Substring 0  LastFolder    ReplaceWith   rawText Substring rawText Length - FileNameLen           If ReplaceWith Length  gt  0 Then             FileNameLen    4             ReplaceWith              End If         textSize   MeasureString rawText  grid Font      Loop      Return rawText End Function  Private Function MeasureString ByVal text As String  ByVal fontInfo As Font  As SizeF     Dim size As SizeF     Dim emSize As Single   fontInfo Size     If emSize   0 Then emSize   12      Dim stringFont As New Font fontInfo Name  emSize       Dim bmp As New Bitmap 1000  100      Dim g As Graphics   Graphics FromImage bmp       size   g MeasureString text  stringFont      g Dispose       Return size End Function

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As pointed above  NET Core 2 x has implementation of Path GetRelativePath    Code below is adapted from sources and works fine with  NET 4 7 1 Framework      Licensed to the  NET Foundation under one or more agreements     The  NET Foundation licenses this file to you under the MIT license     See the LICENSE file in the project root for more information     Adapted from https   github com dotnet corefx blob master src Common src CoreLib System IO Path cs L697    by Anton Krouglov  using System Runtime CompilerServices  using System Diagnostics  using System Text  using Xunit   namespace System IO          Provides methods for processing file system strings in a cross-platform manner         Most of the methods don t do a complete parsing  such as examining a UNC hostname           but they will handle most string operations      public static class PathNetCore                 lt summary gt              Create a relative path from one path to another  Paths will be resolved before calculating the difference              Default path comparison for the active platform will be used  OrdinalIgnoreCase for Windows or Mac  Ordinal for Unix                lt  summary gt               lt param name  relativeTo  gt The source path the output should be relative to  This path is always considered to be a directory  lt  param gt               lt param name  path  gt The destination path  lt  param gt               lt returns gt The relative path or  lt paramref name  path   gt  if the paths don t share the same root  lt  returns gt               lt exception cref  ArgumentNullException  gt Thrown if  lt paramref name  relativeTo   gt  or  lt paramref name  path   gt  is  lt c gt null lt  c gt  or an empty string  lt  exception gt          public static string GetRelativePath string relativeTo  string path                return GetRelativePath relativeTo  path  StringComparison                      private static string GetRelativePath string relativeTo  string path  StringComparison comparisonType                if  string IsNullOrEmpty relativeTo   throw new ArgumentNullException nameof relativeTo                if  string IsNullOrEmpty path   throw new ArgumentNullException nameof path                Debug Assert comparisonType    StringComparison Ordinal                             comparisonType    StringComparison OrdinalIgnoreCase                relativeTo   Path GetFullPath relativeTo               path   Path GetFullPath path                   Need to check if the roots are different- if they are we need to return the  to  path              if   PathInternalNetCore AreRootsEqual relativeTo  path  comparisonType                   return path               int commonLength   PathInternalNetCore GetCommonPathLength relativeTo  path                  ignoreCase  comparisonType    StringComparison OrdinalIgnoreCase                   If there is nothing in common they can t share the same root  return the  to  path as is              if  commonLength    0                  return path                  Trailing separators aren t significant for comparison             int relativeToLength   relativeTo Length              if  PathInternalNetCore EndsInDirectorySeparator relativeTo                   relativeToLength--               bool pathEndsInSeparator   PathInternalNetCore EndsInDirectorySeparator path               int pathLength   path Length              if  pathEndsInSeparator                  pathLength--                  If we have effectively the same path  return                 if  relativeToLength    pathLength  amp  amp  commonLength  gt   relativeToLength  return                      We have the same root  we need to calculate the difference now using the                common Length and Segment count past the length                                Some examples                                 C  Foo C  Bar L3  S1 - gt     Bar                 C  Foo C  Foo Bar L6  S0 - gt  Bar                 C  Foo Bar C  Bar Bar L3  S2 - gt        Bar Bar                 C  Foo Foo C  Foo Bar L7  S1 - gt     Bar              StringBuilder                 sb   new StringBuilder      StringBuilderCache Acquire Math Max relativeTo Length  path Length                    Add parent segments for segments past the common on the  from  path             if  commonLength  lt  relativeToLength                    sb Append                         for  int i   commonLength   1  i  lt  relativeToLength  i                          if  PathInternalNetCore IsDirectorySeparator relativeTo i                              sb Append DirectorySeparatorChar                           sb Append                                                                          else if  PathInternalNetCore IsDirectorySeparator path commonLength                         No parent segments and we need to eat the initial separator                      C  Foo C  Foo Bar case                  commonLength                                  Now add the rest of the  to  path  adding back the trailing separator             int differenceLength   pathLength - commonLength              if  pathEndsInSeparator                  differenceLength                 if  differenceLength  gt  0                    if  sb Length  gt  0                        sb Append DirectorySeparatorChar                                      sb Append path  commonLength  differenceLength                              return sb ToString      StringBuilderCache GetStringAndRelease sb                         Public static readonly variant of the separators  The Path implementation itself is using            internal const variant of the separators for better performance          public static readonly char DirectorySeparatorChar   PathInternalNetCore DirectorySeparatorChar          public static readonly char AltDirectorySeparatorChar   PathInternalNetCore AltDirectorySeparatorChar          public static readonly char VolumeSeparatorChar   PathInternalNetCore VolumeSeparatorChar          public static readonly char PathSeparator   PathInternalNetCore PathSeparator                lt summary gt Returns a comparison that can be used to compare file and directory names for equality  lt  summary gt          internal static StringComparison StringComparison   gt  StringComparison OrdinalIgnoreCase                  lt summary gt Contains internal path helpers that are shared between many projects  lt  summary gt      internal static class PathInternalNetCore           internal const char DirectorySeparatorChar                 internal const char AltDirectorySeparatorChar                internal const char VolumeSeparatorChar                internal const char PathSeparator                 internal const string ExtendedDevicePathPrefix                    internal const string UncPathPrefix                  internal const string UncDevicePrefixToInsert       UNC            internal const string UncExtendedPathPrefix         UNC            internal const string DevicePathPrefix                       internal const int MaxShortPath   260                                       internal const int DevicePrefixLength   4                lt summary gt              Returns true if the two paths have the same root              lt  summary gt          internal static bool AreRootsEqual string first  string second  StringComparison comparisonType                int firstRootLength   GetRootLength first               int secondRootLength   GetRootLength second                return firstRootLength    secondRootLength                     amp  amp  string Compare                         strA  first                         indexA  0                         strB  second                         indexB  0                         length  firstRootLength                         comparisonType  comparisonType     0                          lt summary gt              Gets the length of the root of the path  drive  share  etc                 lt  summary gt          internal static int GetRootLength string path                int i   0              int volumeSeparatorLength   2     Length to the colon  C               int uncRootLength   2     Length to the start of the server name                   bool extendedSyntax   path StartsWith ExtendedDevicePathPrefix               bool extendedUncSyntax   path StartsWith UncExtendedPathPrefix               if  extendedSyntax                       Shift the position we look for the root from to account for the extended prefix                 if  extendedUncSyntax                                - gt       UNC                       uncRootLength   UncExtendedPathPrefix Length                                    else                           C   - gt       C                       volumeSeparatorLength    ExtendedDevicePathPrefix Length                                               if    extendedSyntax    extendedUncSyntax   amp  amp  path Length  gt  0  amp  amp  IsDirectorySeparator path 0                         UNC or simple rooted path  e g    foo   NOT      C  foo                    i   1      Drive rooted   foo  is one character                 if  extendedUncSyntax     path Length  gt  1  amp  amp  IsDirectorySeparator path 1                              UNC      UNC  or      scan past the next two directory separators at most                         e g  to     UNC Server Share or   Server Share                       i   uncRootLength                      int n   2     Maximum separators to skip                     while  i  lt  path Length  amp  amp    IsDirectorySeparator path i      --n  gt  0   i                                                else if  path Length  gt   volumeSeparatorLength  amp  amp                       path volumeSeparatorLength - 1     PathNetCore VolumeSeparatorChar                       Path is at least longer than where we expect a colon  and has a colon      A   A                      If the colon is followed by a directory separator  move past it                 i   volumeSeparatorLength                  if  path Length  gt   volumeSeparatorLength   1  amp  amp  IsDirectorySeparator path volumeSeparatorLength    i                               return i                          lt summary gt              True if the given character is a directory separator               lt  summary gt           MethodImpl MethodImplOptions AggressiveInlining           internal static bool IsDirectorySeparator char c                return c    PathNetCore DirectorySeparatorChar    c    PathNetCore AltDirectorySeparatorChar                          lt summary gt              Get the common path length from the start of the string               lt  summary gt          internal static int GetCommonPathLength string first  string second  bool ignoreCase                int commonChars   EqualStartingCharacterCount first  second  ignoreCase  ignoreCase                   If nothing matches             if  commonChars    0                  return commonChars                  Or we re a full string and equal length or match to a separator             if  commonChars    first Length                  amp  amp   commonChars    second Length    IsDirectorySeparator second commonChars                     return commonChars               if  commonChars    second Length  amp  amp  IsDirectorySeparator first commonChars                    return commonChars                  It s possible we matched somewhere in the middle of a segment e g  C  Foodie and C  Foobar              while  commonChars  gt  0  amp  amp   IsDirectorySeparator first commonChars - 1                    commonChars--               return commonChars                          lt summary gt              Gets the count of common characters from the left optionally ignoring case              lt  summary gt          internal static unsafe int EqualStartingCharacterCount string first  string second  bool ignoreCase                if  string IsNullOrEmpty first     string IsNullOrEmpty second   return 0               int commonChars   0               fixed  char  f   first              fixed  char  s   second                    char  l   f                  char  r   s                  char  leftEnd   l   first Length                  char  rightEnd   r   second Length                   while  l    leftEnd  amp  amp  r    rightEnd                                      amp  amp    l     r     ignoreCase  amp  amp                                                       char ToUpperInvariant   l      char ToUpperInvariant   r                            commonChars                        l                        r                                                 return commonChars                          lt summary gt              Returns true if the path ends in a directory separator               lt  summary gt          internal static bool EndsInDirectorySeparator string path                gt  path Length  gt  0  amp  amp  IsDirectorySeparator path path Length - 1                    lt summary gt  Tests for PathNetCore GetRelativePath  lt  summary gt      public static class GetRelativePathTests            Theory           InlineData   C       C                     InlineData   C  a     C  a                    InlineData   C  A     C  a                    InlineData   C  a      C  a                   InlineData   C       C  b     b             InlineData   C  a     C  b        b             InlineData   C  a     C  b         b              InlineData   C  a b     C  a                    InlineData   C  a b     C  a                     InlineData   C  a b      C  a                    InlineData   C  a b      C  a                     InlineData   C  a b c     C  a b                    InlineData   C  a b c     C  a b                     InlineData   C  a b c     C  a                       InlineData   C  a b c     C  a                        InlineData   C  a b c      C  a b                    InlineData   C  a b c      C  a b                     InlineData   C  a b c      C  a                       InlineData   C  a b c      C  a                        InlineData   C  a      C  b        b             InlineData   C  a     C  a b     b             InlineData   C  a     C  A b     b             InlineData   C  a     C  b c        b c             InlineData   C  a      C  a b     b             InlineData   C       D       D               InlineData   C       D  b     D  b             InlineData   C       D  b      D  b              InlineData   C  a     D  b     D  b             InlineData   C  a      D  b     D  b             InlineData   C  ab     C  a        a             InlineData   C  a     C  ab        ab             InlineData   C         LOCALHOST Share b       LOCALHOST Share b             InlineData     LOCALHOST Share a       LOCALHOST Share b        b               PlatformSpecific TestPlatforms Windows       Tests Windows-specific paths         public static void GetRelativePath Windows string relativeTo  string path  string expected                string result   PathNetCore GetRelativePath relativeTo  path               Assert Equal expected  result                   Check that we get the equivalent path when the result is combined with the sources             Assert Equal                  Path GetFullPath path  TrimEnd Path DirectorySeparatorChar                   Path GetFullPath Path Combine Path GetFullPath relativeTo   result                        TrimEnd Path DirectorySeparatorChar                   ignoreCase  true                  ignoreLineEndingDifferences  false                  ignoreWhiteSpaceDifferences  false

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Play with something like   private String GetRelativePath Int32 level  String directory  out String errorMessage            if  level  lt  0    level  gt  5                errorMessage    Find some more smart input data               return String Empty                                                          while  level    0                directory   Path GetDirectoryName directory               level -  1                                                          errorMessage   String Empty          return directory          And test it   Test      public void RelativeDirectoryPathTest             var relativePath               GetRelativePath 3  AppDomain CurrentDomain BaseDirectory  out var errorMessage           Console WriteLine relativePath           if  String IsNullOrEmpty errorMessage     false                Console WriteLine errorMessage               Assert Fail  Can not find relative path

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This should work   private string rel string path      string   cwd    new Regex          Split Directory GetCurrentDirectory       string   fp     new Regex          Split path      int common   0     for  int n   0  n  lt  fp Length  n          if  n  lt  cwd Length  amp  amp  n  lt  fp Length  amp  amp  cwd n     fp n           common                 if  common  gt  0        List lt string gt  rp   new List lt string gt          for  int n   0  n  lt   cwd Length - common   n            rp Add                   for  int n   common  n  lt  fp Length  n            rp Add fp n               return String Join      rp ToArray         else       return String Join      fp

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public static string ToRelativePath string filePath  string refPath                var pathNormalized   Path GetFullPath filePath            var refNormalized   Path GetFullPath refPath           refNormalized   refNormalized TrimEnd                      if   pathNormalized StartsWith refNormalized               throw new ArgumentException            var res   pathNormalized Substring refNormalized Length   1           return res

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If you re sure that your absolute path 2 is always relative to absolute path  just remove the first N characters from path2  where N is the length of path1

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A bit late to the question  but I just needed this feature as well   I agree with DavidK that since there is a built-in API function that provides this  you should use it   Here s a managed wrapper for it   public static string GetRelativePath string fromPath  string toPath        int fromAttr   GetPathAttribute fromPath       int toAttr   GetPathAttribute toPath        StringBuilder path   new StringBuilder 260      MAX PATH     if PathRelativePathTo          path          fromPath          fromAttr          toPath          toAttr     0                throw new ArgumentException  Paths must have a common prefix              return path ToString       private static int GetPathAttribute string path        DirectoryInfo di   new DirectoryInfo path       if  di Exists                return FILE ATTRIBUTE DIRECTORY             FileInfo fi   new FileInfo path       if fi Exists                return FILE ATTRIBUTE NORMAL             throw new FileNotFoundException       private const int FILE ATTRIBUTE DIRECTORY   0x10  private const int FILE ATTRIBUTE NORMAL   0x80    DllImport  shlwapi dll   SetLastError   true   private static extern int PathRelativePathTo StringBuilder pszPath       string pszFrom  int dwAttrFrom  string pszTo  int dwAttrTo

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As Alex Brault points out  especially on Windows  the absolute path  with drive letter and all  is unambiguous and often better   Shouldn t your OpenFileDialog use a regular tree-browser structure   To get some nomenclature in place  the RefDir is the directory relative to which you want to specify the path  the AbsName is the absolute path name that you want to map  and the RelPath is the resulting relative path   Take the first of these options that matches    If you have different drive letters  there is no relative path from RefDir to AbsName  you must use the AbsName  If the AbsName is in a sub-directory of RefDir or is a file within RefDir then simply remove the RefDir from the start of AbsName to create RelPath  optionally prepend       or      since you are on Windows   Find the longest common prefix of RefDir and AbsName  where D  Abc Def and D  Abc Default share D  Abc as the longest common prefix  it has to be a mapping of name components  not a simple longest common substring   call it LCP   Remove LCP from AbsName and RefDir   For each path component left in  RefDir - LCP   prepend       to  AbsName - LCP  to yield RelPath    To illustrate the last rule  which is  of course  by far the most complex   start with   RefDir   D  Abc Def Ghi AbsName   D  Abc Default Karma Crucible   Then  LCP   D  Abc  RefDir - LCP    Def Ghi  Absname - LCP    Default Karma Crucible RelPath         Default Karma Crucible   While I was typing  DavidK produced an answer which suggests that you are not the first to need this feature and that there is a standard function to do this job   Use it   But there s no harm in being able to think your way through from first principles  either   Except that Unix systems do not support drive letters  so everything is always located under the same root directory  and the first bullet therefore is irrelevant   the same technique could be used on Unix

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Way with Uri not worked on linux macOS systems  Path   var www root  can t be converted to Uri  More universal way - do all by hands   public static string MakeRelativePath string fromPath  string toPath  string sep              var fromParts   fromPath Split new                         StringSplitOptions RemoveEmptyEntries       var toParts   toPath Split new                         StringSplitOptions RemoveEmptyEntries        var matchedParts   fromParts          Zip toParts   x  y    gt  string Compare x  y  true     0           TakeWhile x   gt  x  Count         return string Join     Enumerable Range 0  fromParts Length - matchedParts           Select x   gt         sep                 string Join sep  toParts Skip matchedParts                PS  i use     as a default value of separator instead of Path DirectorySeparatorChar  because result of this method used as uri in my app

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If you re sure that your absolute path 2 is always relative to absolute path  just remove the first N characters from path2  where N is the length of path1

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I d split both of your paths at the directory level  From there  find the point of divergence and work your way back to the assembly folder  prepending a       everytime you pass a directory   Keep in mind however  that an absolute path works everywhere and is usually easier to read than a relative one  I personally wouldn t show an user a relative path unless it was absolutely necessary

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As Alex Brault points out  especially on Windows  the absolute path  with drive letter and all  is unambiguous and often better   Shouldn t your OpenFileDialog use a regular tree-browser structure   To get some nomenclature in place  the RefDir is the directory relative to which you want to specify the path  the AbsName is the absolute path name that you want to map  and the RelPath is the resulting relative path   Take the first of these options that matches    If you have different drive letters  there is no relative path from RefDir to AbsName  you must use the AbsName  If the AbsName is in a sub-directory of RefDir or is a file within RefDir then simply remove the RefDir from the start of AbsName to create RelPath  optionally prepend       or      since you are on Windows   Find the longest common prefix of RefDir and AbsName  where D  Abc Def and D  Abc Default share D  Abc as the longest common prefix  it has to be a mapping of name components  not a simple longest common substring   call it LCP   Remove LCP from AbsName and RefDir   For each path component left in  RefDir - LCP   prepend       to  AbsName - LCP  to yield RelPath    To illustrate the last rule  which is  of course  by far the most complex   start with   RefDir   D  Abc Def Ghi AbsName   D  Abc Default Karma Crucible   Then  LCP   D  Abc  RefDir - LCP    Def Ghi  Absname - LCP    Default Karma Crucible RelPath         Default Karma Crucible   While I was typing  DavidK produced an answer which suggests that you are not the first to need this feature and that there is a standard function to do this job   Use it   But there s no harm in being able to think your way through from first principles  either   Except that Unix systems do not support drive letters  so everything is always located under the same root directory  and the first bullet therefore is irrelevant   the same technique could be used on Unix

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here s mine   public static string RelativePathTo this System IO DirectoryInfo  this  string to        var rgFrom    this FullName Split new     Path DirectorySeparatorChar  Path AltDirectorySeparatorChar    StringSplitOptions RemoveEmptyEntries       var rgTo   to Split new     Path DirectorySeparatorChar  Path AltDirectorySeparatorChar    StringSplitOptions RemoveEmptyEntries       var cSame   rgFrom TakeWhile  p  i    gt  i  lt  rgTo Length  amp  amp  string Equals p  rgTo i    Count         return Path Combine          Enumerable Range 0  rgFrom Length - cSame           Select     gt                 Concat rgTo Skip cSame            ToArray

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Use   RelPath   AbsPath Replace ApplicationPath

[.net] How to get relative path from absolute path

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