Check if a string is a valid Windows directory folder path

Question

I am trying to determine whether a string input by a user is valid for representing a path to a folder  By valid  I mean formatted properly   In my application  the folder represents an installation destination  Provided that the folder path is valid  I want to determine if the folder exists  and create it if it does not   I am currently using IO Directory Exists  String path    I find that this works fine except when the user does not format the string properly  When that happens  this method will return false which indicates that the folder does not exist  But this is a problem because I won t be able to create the folder afterwards   From my googling I found a suggestion to use a regular expression to check if the format is proper  I have no experience with regular expressions  and am wondering if that is a viable approach  Here s what I found   Regex r   new Regex        a-zA-Z              1       1               lt  gt                return r IsMatch  path      Would a regular expression test in combination with Directory Exists    give me a good enough method to check if the path is valid and whether it exists  I know this will vary with the OS and other factors  but the program is targeted for Windows users only

User · Answer

Here is a solution that leverages the use of Path.GetFullPath as recommended in the answer by @SLaks.

In the code that I am including here, note that IsValidPath(string path) is designed such that the caller does not have to worry about exception handling.

You may also find that the method that it calls, TryGetFullPath(...), also has merit on its own when you wish to safely attempt to get an absolute path.

/// <summary>
/// Gets a value that indicates whether <paramref name="path"/>
/// is a valid path.
/// </summary>
/// <returns>Returns <c>true</c> if <paramref name="path"/> is a
/// valid path; <c>false</c> otherwise. Also returns <c>false</c> if
/// the caller does not have the required permissions to access
/// <paramref name="path"/>.
/// </returns>
/// <seealso cref="Path.GetFullPath"/>
/// <seealso cref="TryGetFullPath"/>
public static bool IsValidPath(string path)
{
    string result;
    return TryGetFullPath(path, out result);
}

/// <summary>
/// Returns the absolute path for the specified path string. A return
/// value indicates whether the conversion succeeded.
/// </summary>
/// <param name="path">The file or directory for which to obtain absolute
/// path information.
/// </param>
/// <param name="result">When this method returns, contains the absolute
/// path representation of <paramref name="path"/>, if the conversion
/// succeeded, or <see cref="String.Empty"/> if the conversion failed.
/// The conversion fails if <paramref name="path"/> is null or
/// <see cref="String.Empty"/>, or is not of the correct format. This
/// parameter is passed uninitialized; any value originally supplied
/// in <paramref name="result"/> will be overwritten.
/// </param>
/// <returns><c>true</c> if <paramref name="path"/> was converted
/// to an absolute path successfully; otherwise, false.
/// </returns>
/// <seealso cref="Path.GetFullPath"/>
/// <seealso cref="IsValidPath"/>
public static bool TryGetFullPath(string path, out string result)
{
    result = String.Empty;
    if (String.IsNullOrWhiteSpace(path)) { return false; }
    bool status = false;

    try
    {
        result = Path.GetFullPath(path);
        status = true;
    }
    catch (ArgumentException) { }
    catch (SecurityException) { }
    catch (NotSupportedException) { }
    catch (PathTooLongException) { }

    return status;
}

User · Answer

I haven t had any problems with this code   private bool IsValidPath string path  bool exactPath   true        bool isValid   true       try               string fullPath   Path GetFullPath path            if  exactPath                        string root   Path GetPathRoot path               isValid   string IsNullOrEmpty root Trim new char                      false                    else                       isValid   Path IsPathRooted path                       catch Exception ex                isValid   false             return isValid      For example these would return false   IsValidPath  C  abc d    IsValidPath  C  abc d    IsValidPath  C  abc  d    IsValidPath  C  abc lt d    IsValidPath  C  abc gt d    IsValidPath  C  abc d    IsValidPath  C  abc d    IsValidPath      IsValidPath    abc    IsValidPath   abc    IsValidPath  abc    IsValidPath  abc   false     And these would return true   IsValidPath   C   abc    IsValidPath   F  FILES     IsValidPath   C   abc docx  defg docx    IsValidPath   C  abc defg    IsValidPath   C               abc                 defg    IsValidPath   C  abc def         amp    -          g    IsValidPath   C      abc        defg    IsValidPath    abc   false

User · Answer

A simpler OS-independent solution  Go ahead and attempt to create the actual directory  if there is an issue or the name is invalid  the OS will automatically complain and the code will throw  public static class PathHelper       public static void ValidatePath string path                if   Directory Exists path               Directory CreateDirectory path  Delete             Usage  try       PathHelper ValidatePath path     catch Exception e           handle exception    Directory CreateDirectory   will automatically throw in all of the following situations   System IO IOException  The directory specified by path is a file  -or- The network name is not known  System UnauthorizedAccessException  The caller does not have the required permission  System ArgumentException  path is a zero-length string  contains only white space  or contains one or more   invalid characters  You can query for invalid characters by using the System IO Path GetInvalidPathChars   method  -or- path is prefixed with  or contains  only a colon character      System ArgumentNullException  path is null  System IO PathTooLongException  The specified path  file name  or both exceed the system-defined maximum length  System IO DirectoryNotFoundException  The specified path is invalid  for example  it is on an unmapped drive   System NotSupportedException  path contains a colon character     that is not part of a drive label   quot C  quot

User · Answer

Path GetFullPath gives below exceptions only     ArgumentException  path is a zero-length string  contains only white   space  or contains one or more of the invalid characters defined in   GetInvalidPathChars    -or- The system could not retrieve the absolute path       SecurityException  The caller does not have the required permissions       ArgumentNullException  path is null       NotSupportedException  path contains a colon       that is not part of   a volume identifier  for example   c           PathTooLongException   The specified path  file name  or both exceed   the system-defined maximum length  For example  on Windows-based   platforms  paths must be less than 248 characters  and file names must   be less than 260 characters    Alternate way is to use the following         lt summary gt      Validate the Path  If path is relative append the path to the project directory by default       lt  summary gt       lt param name  path  gt Path to validate lt  param gt       lt param name  RelativePath  gt Relative path lt  param gt       lt param name  Extension  gt If want to check for File Path lt  param gt       lt returns gt  lt  returns gt  private static bool ValidateDllPath ref string path  string RelativePath       string Extension                Check if it contains any Invalid Characters      if  path IndexOfAny Path GetInvalidPathChars       -1                try                          If path is relative take  IGXLROOT  as the base directory             if   Path IsPathRooted path                                 if  string IsNullOrEmpty RelativePath                                            Exceptions handled by Path GetFullPath                        ArgumentException path is a zero-length string  contains only white space  or contains one or more of the invalid characters defined in GetInvalidPathChars  -or- The system could not retrieve the absolute path                                                 SecurityException The caller does not have the required permissions                                                 ArgumentNullException path is null                                                 NotSupportedException path contains a colon       that is not part of a volume identifier  for example   c                              PathTooLongException The specified path  file name  or both exceed the system-defined maximum length  For example  on Windows-based platforms  paths must be less than 248 characters  and file names must be less than 260 characters                          RelativePath is not passed so we would take the project path                      path   Path GetFullPath RelativePath                                      else                                          Make sure the path is relative to the RelativePath and not our project directory                     path   Path Combine RelativePath  path                                                   Exceptions from FileInfo Constructor                   System ArgumentNullException                     fileName is null                                  System Security SecurityException                     The caller does not have the required permission                                  System ArgumentException                     The file name is empty  contains only white spaces  or contains invalid characters                                  System IO PathTooLongException                     The specified path  file name  or both exceed the system-defined maximum                    length  For example  on Windows-based platforms  paths must be less than                    248 characters  and file names must be less than 260 characters                                  System NotSupportedException                     fileName contains a colon     in the middle of the string              FileInfo fileInfo   new FileInfo path                   Exceptions using FileInfo Length                   System IO IOException                     System IO FileSystemInfo Refresh   cannot update the state of the file or                    directory                                  System IO FileNotFoundException                     The file does not exist -or- The Length property is called for a directory              bool throwEx   fileInfo Length    -1                  Exceptions using FileInfo IsReadOnly                   System UnauthorizedAccessException                     Access to fileName is denied                     The file described by the current System IO FileInfo object is read-only -or-                    This operation is not supported on the current platform -or- The caller does                    not have the required permission              throwEx   fileInfo IsReadOnly               if   string IsNullOrEmpty Extension                                    Validate the Extension of the file                  if  Path GetExtension path  Equals Extension  StringComparison InvariantCultureIgnoreCase                                            Trim the Library Path                     path   path Trim                        return true                                    else                                       return false                                              else                               return true                                   catch  ArgumentNullException                             System ArgumentNullException                     fileName is null                    catch  System Security SecurityException                             System Security SecurityException                     The caller does not have the required permission                    catch  ArgumentException                             System ArgumentException                     The file name is empty  contains only white spaces  or contains invalid characters                    catch  UnauthorizedAccessException                             System UnauthorizedAccessException                     Access to fileName is denied                    catch  PathTooLongException                             System IO PathTooLongException                     The specified path  file name  or both exceed the system-defined maximum                    length  For example  on Windows-based platforms  paths must be less than                    248 characters  and file names must be less than 260 characters                    catch  NotSupportedException                             System NotSupportedException                     fileName contains a colon     in the middle of the string                    catch  FileNotFoundException                           System FileNotFoundException                 The exception that is thrown when an attempt to access a file that does not                 exist on disk fails                    catch  IOException                             System IO IOException                     An I O error occurred while opening the file                    catch  Exception                           Unknown Exception  Might be due to wrong case or nulll checks                      else                  Path contains invalid characters           return false

User · Answer

I actually disagree with SLaks  That solution did not work for me  Exception did not happen as expected  But this code worked for me    if System IO Directory Exists path

User · Answer

Use this Code  string DirectoryName    Sample Name For Directory Or File   Path GetInvalidFileNameChars      Where x   gt  DirectoryName Contains x      Count    gt  0    DirectoryName     con

User · Answer

private bool IsValidPath string path                Regex driveCheck   new Regex     a-zA-Z                 if   driveCheck IsMatch path Substring 0  3    return false          string strTheseAreInvalidFileNameChars   new string Path GetInvalidPathChars             strTheseAreInvalidFileNameChars                            Regex containsABadCharacter   new Regex       Regex Escape strTheseAreInvalidFileNameChars                  if  containsABadCharacter IsMatch path Substring 3  path Length - 3                return false           DirectoryInfo dir   new DirectoryInfo Path GetFullPath path            if   dir Exists              dir Create            return true

User · Answer

Call Path GetFullPath  it will throw exceptions if the path is invalid   To disallow relative paths  such as Word   call  Path IsPathRooted

[c#] Check if a string is a valid Windows directory (folder) path

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