Replace multiple characters in a C string

Question

Is there a better way to replace strings   I am surprised that Replace does not take in a character array or string array   I guess that I could write my own extension but I was curious if there is a better built in way to do the following   Notice the last Replace is a string not a character   myString Replace        n   Replace        n   Replace   r     n   Replace   t     n   Replace        n   Replace   n n     n

User · Answer

Use RegEx Replace  something like this     string input    This is   text with   far  too   much                          whitespace      string pattern             string replacement     n     Regex rgx   new Regex pattern     string result   rgx Replace input  replacement     Here s more info on this MSDN documentation for RegEx Replace

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You may also simply write these string extension methods  and put them somewhere in your solution   using System Text   public static class StringExtensions       public static string ReplaceAll this string original  string toBeReplaced  string newValue                if  string IsNullOrEmpty original     string IsNullOrEmpty toBeReplaced   return original          if  newValue    null  newValue   string Empty          StringBuilder sb   new StringBuilder            foreach  char ch in original                        if  toBeReplaced IndexOf ch   lt  0  sb Append ch               else sb Append newValue                     return sb ToString               public static string ReplaceAll this string original  string   toBeReplaced  string newValue                if  string IsNullOrEmpty original     toBeReplaced    null    toBeReplaced Length  lt   0  return original          if  newValue    null  newValue   string Empty          foreach  string str in toBeReplaced              if   string IsNullOrEmpty str                   original   original Replace str  newValue           return original             Call them like this    ABCDE  ReplaceAll  ACE    xy         xyBxyDxy    And this    ABCDEF  ReplaceAll new string      AB    DE    EF      xy         xyCxyF

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You can use a replace regular expression   s     t r     n  2   n g    s  at the beginning means a search The characters between   and   are the characters to search for  in any order  The second   delimits the search-for text and the replace text   In English  this reads    Search for   or   or  t or  r or   space  or exactly two sequential  n and replace it with  n   In C   you could do the following   after importing System Text RegularExpressions   Regex pattern   new Regex      t r     n  2     pattern Replace myString    n

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Strings are just immutable char arrays You just need to make it mutable   either by using StringBuilder go in the unsafe world and play with pointers  dangerous though   and try to iterate through the array of characters the least amount of times  Note the HashSet here  as it avoids to traverse the character sequence inside the loop  Should you need an even faster lookup  you can replace HashSet by an optimized lookup for char  based on an array 256    Example with StringBuilder public static void MultiReplace this StringBuilder builder       char   toReplace       char replacement        HashSet lt char gt  set   new HashSet lt char gt  toReplace       for  int i   0  i  lt  builder Length    i                var currentCharacter   builder i           if  set Contains currentCharacter                         builder i    replacement                     Edit - Optimized version public static void MultiReplace this StringBuilder builder       char   toReplace      char replacement        var set   new bool 256       foreach  var charToReplace in toReplace                set charToReplace    true            for  int i   0  i  lt  builder Length    i                var currentCharacter   builder i           if  set currentCharacter                         builder i    replacement                     Then you just use it like this  var builder   new StringBuilder  quot my bad url amp slugs quot    builder MultiReplace new           amp           -    var result   builder ToString

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I know this question is super old  but I want to offer 2 options that are more efficient  1st off  the extension method posted by Paul Walls is good but can be made more efficient by using the StringBuilder class  which is like the string data type but made especially for situations where you will be changing string values more than once  Here is a version I made of the extension method using StringBuilder  public static string ReplaceChars this string s  char   separators  char newVal        StringBuilder sb   new StringBuilder s       foreach  var c in separators    sb Replace c  newVal         return sb ToString       I ran this operation 100 000 times and using StringBuilder took 73ms compared to 81ms using string  So the difference is typically negligible  unless you re running many operations or using a huge string  Secondly  here is a 1 liner loop you can use  foreach  char c in separators    s   s Replace c    n       I personally think this is the best option  It is highly efficient and doesn t require writing an extension method  In my testing this ran the 100k iterations in only 63ms  making it the most efficient  Here is an example in context  string s    quot this is  ra t n n ntest quot   char   separators   new char                      r     t     n     foreach  char c in separators    s   s Replace c    n       Credit to Paul Walls for the first 2 lines in this example

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You could use Linq s Aggregate function   string s    the nquick tbrown rdog jumped over the lazy fox    char   chars   new char                      r     t     n     string snew   chars Aggregate s   c1  c2    gt  c1 Replace c2    n       Here s the extension method   public static string ReplaceAll this string seed  char   chars  char replacementCharacter        return chars Aggregate seed   str  cItem    gt  str Replace cItem  replacementCharacter        Extension method usage example   string snew   s ReplaceAll chars    n

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Ohhh  the performance horror  The answer is a bit outdated  but still     public static class StringUtils        region Private members       ThreadStatic      private static StringBuilder m ReplaceSB       private static StringBuilder GetReplaceSB int capacity                var result   m ReplaceSB           if  null    result                        result   new StringBuilder capacity               m ReplaceSB   result                    else                       result Clear                result EnsureCapacity capacity                      return result              public static string ReplaceAny this string s  char replaceWith  params char   chars                if  null    chars              return s           if  null    s              return null           StringBuilder sb   null           for  int i   0  count   s Length  i  lt  count  i                          var temp   s i               var replace   false               for  int j   0  cc   chars Length  j  lt  cc  j                    if  temp    chars j                                         if  null    sb                                                sb   GetReplaceSB count                           if  i  gt  0                              sb Append s  0  i                                              replace   true                      break                                 if  replace                  sb Append replaceWith               else                 if  null    sb                      sb Append temp                      return null    sb   s   sb ToString

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Performance-Wise this probably might not be the best solution but it works   var str    filename with amp bad separators txt   char   charArray   new char                 amp                      lt      gt                                                         foreach  var singleChar in charArray       str   str Replace singleChar

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This is the shortest way   myString   Regex Replace myString        t r     n  2      n

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A  NET Core version for replacing a defined set of string chars to a specific char  It leverages the recently introduced Span type and string Create method  The idea is to prepare a replacement array  so no actual comparison operations would be required for the each string char  Thus  the replacement process reminds the way a state machine works  In order to avoid initialization of all items of the replacement array  let s store oldChar   newChar  XOR ed  values there  what gives the following benefits   If a char is not changing  ch   ch   0 - no need to initialize non-changing items The final char can be found by XOR ing  ch   repl ch    ch   0   ch - not changed chars case ch    ch   newChar    newChar - replaced char    So the only requirement would be to ensure that the replacement array is zero-ed when initialized  We ll be using ArrayPool lt char gt  to avoid allocations each time the ReplaceAll method is called  And  in order to ensure that the arrays are zero-ed without expensive call to Array Clear method  we ll be maintaining a pool dedicated for the ReplaceAll method  We ll be clearing the replacement array  exact items only  before returning it to the pool  public static class StringExtensions       private static readonly ArrayPool lt char gt   replacementPool   ArrayPool lt char gt  Create         public static string ReplaceAll this string str  char newChar  params char   oldChars                   If nothing to do  return the original string          if  string IsNullOrEmpty str                 oldChars is null                oldChars Length    0                        return str                        If only one character needs to be replaced             use the more efficient  string Replace           if  oldChars Length    1                        return str Replace oldChars 0   newChar                         Get a replacement array from the pool          var replacements    replacementPool Rent char MaxValue   1            try                          Intialize the replacement array in the way that                all elements represent  oldChar   newChar               foreach  var oldCh in oldChars                                replacements oldCh     char  newChar   oldCh                                 Create a string with replaced characters              return string Create str Length   str  replacements    dst  args    gt                                var repl   args replacements                   foreach  var ch in args str                                        dst 0     char  repl ch    ch                       dst   dst Slice 1                                                       finally                          Clear the replacement array              foreach  var oldCh in oldChars                                replacements oldCh    char MinValue                                Return the replacement array back to the pool               replacementPool Return replacements

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If you are feeling particularly clever and don t want to use Regex   char   separators   new char                 r    t    n     string s    this is  ra t n n ntest   string   temp   s Split separators  StringSplitOptions RemoveEmptyEntries   s   String Join   n   temp     You could wrap this in an extension method with little effort as well   Edit  Or just wait 2 minutes and I ll end up writing it anyway     public static class ExtensionMethods      public static string Replace this string s  char   separators  string newVal              string   temp          temp   s Split separators  StringSplitOptions RemoveEmptyEntries          return String Join  newVal  temp             And voila     char   separators   new char                 r    t    n    string s    this is  ra t n n ntest    s   s Replace separators    n

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string ToBeReplaceCharacters             amp amp     amp quot  amp lt  amp gt          string fileName    filename with lt bad separators     foreach  var RepChar in ToBeReplaceCharacters        fileName   fileName Replace RepChar ToString

[c#] Replace multiple characters in a C# string

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