How to remove certain characters from a string in C

Question

For example I have a user input a phone number   cout  lt  lt   Enter phone number     INPUT   555  555-5555 cin  gt  gt  phone    I want to remove the           and  -  characters from the string  I ve looked at the string remove  find and replace functions however I only see that they operate based on position   Is there a string function that I can use to pass a character      for example  and have it remove all instances within a string

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using namespace std       c  03 string s     555  555-5555   s erase remove if s begin    s end    not1 ptr fun   isdigit     s end         c  11 s erase remove if s begin    s end    ptr fun   ispunct    s end       Note  It s posible you need write ptr fun lt int  int gt  rather than simple ptr fun

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For those of you that prefer a more concise  easier to read lambda coding style     This example removes all non-alphanumeric and white space characters from a wide string  You can mix it up with any of the other ctype h helper functions to remove complex-looking character-based tests     I m not sure how these functions would handle CJK languages  so walk softly there           Boring C loops   for int i 0 i lt str size   i             Boring C   eqivalent   for iterator iter c begin  iter    c end    iter     See if you don t find this easier to understand than noisy C C   for iterator loops   TSTRING label    T  1    Replen  amp  Move  RPMV    TSTRING newLabel   label  set lt TCHAR gt  badChars     Use ispunct  isalpha  isdigit  et al   lambda version  with capture list parameter s  example  handiest thing since sliced bread  for each label begin    label end      amp badChars  TCHAR n       if   isalpha n   amp  amp   isdigit n           badChars insert n        for each badChars begin    badChars end      amp newLabel  TCHAR n       newLabel erase std  remove newLabel begin    newLabel end    n   newLabel end           newLabel results after running this code   1ReplenMoveRPMV   This is just academic  since it would clearly be more precise  concise and efficient to combine the  if  logic from lambda0  first for each  into the single lambda1  second for each   if you have already established which characters are the  badChars

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Here s yet another alternative   template lt typename T gt  void Remove  std  basic string lt T gt   amp  Str  const T   CharsToRemove         std  basic string lt T gt   size type pos   0      while    pos   Str find first of  CharsToRemove  pos       std  basic string lt T gt   npos                 Str erase  pos  1              std  string a    555  555-5555    Remove  a     -      Works with std  string and std  wstring

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Using std  wstring and wchar t  requires the Unicode header       include  lt tchar h gt  std  wstring phone L  555  555-5555         fancy static range initializer next  not necessary to setup badChars2 this exact same way   It s overkill  more academic than anything else   const wchar t  tmp   L   -    const std  set lt wchar t gt  badChars2 tmp tmp   sizeof tmp -1     Simple  concise lambda    Uses phone in the lambda capture list  Uses Erase-remove idiom Removes all bad characters from phone   for each badChars2 begin    badChars2 end      amp phone  wchar t n        phone erase std  remove phone begin    phone end    n   phone end         wcout  lt  lt  phone  lt  lt  endl     Output   555 5555555

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If you have access to a compiler that supports variadic templates  you can use this    include  lt iostream gt   include  lt string gt   include  lt algorithm gt   template lt char     CharacterList gt  inline bool check characters char c        char match characters sizeof    CharacterList       CharacterList           for int i   0  i  lt  sizeof    CharacterList     i            if c    match characters i                 return true                      return false     template lt char     CharacterList gt  inline void strip characters std  string  amp  str        str erase std  remove if str begin    str end     amp check characters lt CharacterList    gt    str end        int main         std  string str   555  555-5555        strip characters lt           -   gt  str       std  cout  lt  lt  str  lt  lt  std  endl

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I m new  but some of the answers above are insanely complicated  so here s an alternative    NOTE  As long as 0-9 are contiguous  which they should be according to the standard   this should filter out all other characters but numbers and      Knowing 0-9 should be contiguous and a char is really an int  we can do the below   EDIT  I didn t notice the poster wanted spaces too  so I altered it      include  lt cstdio gt   include  lt cstring gt   void numfilter char   buff  const char   string      do        According to standard  0-9 should be contiguous in system int value      if     string  gt    0   amp  amp   string  lt    9       string                buff      string      while      string       buff       0      Null terminate    int main       const char  string     555  555-5555     char buff  strlen string    1       numfilter buff  string     printf   s n   buff    return 0      Below is to filter supplied characters    include  lt cstdio gt   include  lt cstring gt   void cfilter char   buff  const char   string  const char   toks      const char   tmp      So we can keep toks pointer addr    do         tmp   toks       buff      string     Assume it s correct and place it      do                    I can t think of a faster way              if   string     tmp                  buff--      Not correct  pull back and move on          break               while     tmp      while     string       buff       0       Null terminate    int main       char   string     555  555-5555     char   toks      -     char buff  strlen string    1       cfilter buff  string  toks     printf   s n   buff      return 0

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string str   555  555-5555        char chars        -       for  unsigned int i   0  i  lt  strlen chars     i                you need include  lt algorithm gt  to use general algorithms like std  remove         str erase  std  remove str begin    str end    chars i    str end                 output  555 5555555    cout  lt  lt  str  lt  lt  endl    To use as function   void removeCharsFromString  string  amp str  char  charsToRemove        for   unsigned int i   0  i  lt  strlen charsToRemove     i           str erase  remove str begin    str end    charsToRemove i    str end               example of usage  removeCharsFromString  str     -

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I want to remove the           and  -    characters from the string    You can use the std  remove if   algorithm to remove only the characters you specify    include  lt iostream gt   include  lt algorithm gt   include  lt string gt   bool IsParenthesesOrDash char c        switch c            case          case          case  -           return true      default          return false           int main         std  string str   555  555-5555        str erase std  remove if str begin    str end     amp IsParenthesesOrDash   str end         std  cout  lt  lt  str  lt  lt  std  endl     Expected output  555 5555555     The std  remove if   algorithm requires something called a predicate  which can be a function pointer like the snippet above   You can also pass a function object  an object that overloads the function call    operator   This allows us to create an even more general solution    include  lt iostream gt   include  lt algorithm gt   include  lt string gt   class IsChars   public      IsChars const char  charsToRemove    chars charsToRemove           bool operator   char c                for const char  testChar   chars   testChar    0    testChar                        if  testChar    c    return true                      return false         private      const char  chars      int main         std  string str   555  555-5555        str erase std  remove if str begin    str end    IsChars    -      str end         std  cout  lt  lt  str  lt  lt  std  endl     Expected output  5555555555     You can specify what characters to remove with the    -   string  In the example above I added a space so that spaces are removed as well as parentheses and dashes

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Lot of good answers  here is another way to clean up a string of numbers  is not deleting chars but by moving the numbers out   string str   555  555-5555    clean  for  char c   str      if  c  gt   48 and c  lt   57          clean push back c

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I m afraid there is no such a member for std  string  but you can easily program that kind of functions  It may not be the fastest solution but this would suffice   std  string RemoveChars const std  string amp  source  const std  string amp  chars       std  string result        for  unsigned int i 0  i lt source length    i            bool foundany false        for  unsigned int j 0  j lt chars length    amp  amp   foundany  j               foundany  source i   chars j                  if   foundany             result  source i                   return result      EDIT  Reading the answer below  I understood it to be more general  not only to detect digit  The above solution will omit every character passed in the second argument string  For example   std  string result RemoveChars   999 99-8765-43 87      -      Will result in  99999876543 87

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Yes  you can use the isdigit   function to check for a digits     Here you go    include  lt iostream gt   include  lt cctype gt   include  lt string h gt   using namespace std   int main       char  str     555  555-5555     int len   strlen str      for  int i 0  i lt len  i           if  isdigit   str i             cout  lt  lt    str i                  cout  lt  lt  endl    return 0         Hope it helps

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remove if   has already been mentioned  But  with C  0x  you can specify the predicate for it with a lambda instead   Below is an example of that with 3 different ways of doing the filtering   copy  versions of the functions are included too for cases when you re working with a const or don t want to modify the original    include  lt iostream gt   include  lt string gt   include  lt algorithm gt   include  lt cctype gt  using namespace std   string amp  remove chars string amp  s  const string amp  chars        s erase remove if s begin    s end      amp chars  const char amp  c            return chars find c     string  npos          s end         return s    string remove chars copy string s  const string amp  chars        return remove chars s  chars      string amp  remove nondigit string amp  s        s erase remove if s begin    s end       const char amp  c            return  isdigit c           s end         return s    string remove nondigit copy string s        return remove nondigit s      string amp  remove chars if not string amp  s  const string amp  allowed        s erase remove if s begin    s end      amp allowed  const char amp  c            return allowed find c     string  npos          s end         return s    string remove chars if not copy string s  const string amp  allowed        return remove chars if not s  allowed      int main         const string test1   555  555-5555        string test2 test1       string test3 test1       string test4 test1       cout  lt  lt  remove chars copy test1     -     lt  lt  endl      cout  lt  lt  remove chars test2     -     lt  lt  endl      cout  lt  lt  remove nondigit copy test1   lt  lt  endl      cout  lt  lt  remove nondigit test3   lt  lt  endl      cout  lt  lt  remove chars if not copy test1   0123456789    lt  lt  endl      cout  lt  lt  remove chars if not test4   0123456789    lt  lt  endl

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Here is a different solution for anyone interested  It uses the new For range in c  11  string str   555  555-5555    string str2      for  const auto c  str        if  ispunct c             str2 push back c            str   str2    output  555 5555555 cout lt  lt str lt  lt endl

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boost  is any of  Strip for all characters from one string that appear in another given string    include  lt cassert gt    include  lt boost range algorithm remove if hpp gt   include  lt boost algorithm string classification hpp gt   int main         std  string str    a bc0 d       str erase boost  remove if str  boost  is any of   0     str end         assert  str     abcd         Tested in Ubuntu 16 04  Boost 1 58

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