Replace substring with another substring C

Question

How could I replace a substring in a string with another substring in C    what functions could I use    eg  string test    abc def abc def   test replace  abc    hij   replace  def    klm      replace occurrence of abc and def with other substring

User · Answer

Here is a solution I wrote using the builder tactic:

#include <string>
#include <sstream>

using std::string;
using std::stringstream;

string stringReplace (const string& source,
                      const string& toReplace,
                      const string& replaceWith)
{
  size_t pos = 0;
  size_t cursor = 0;
  int repLen = toReplace.length();
  stringstream builder;

  do
  {
    pos = source.find(toReplace, cursor);

    if (string::npos != pos)
    {
        //copy up to the match, then append the replacement
        builder << source.substr(cursor, pos - cursor);
        builder << replaceWith;

        // skip past the match 
        cursor = pos + repLen;
    }
  } 
  while (string::npos != pos);

  //copy the remainder
  builder << source.substr(cursor);

  return (builder.str());
}

Tests:

void addTestResult (const string&& testId, bool pass)
{
  ...
}

void testStringReplace()
{
    string source = "123456789012345678901234567890";
    string toReplace = "567";
    string replaceWith = "abcd";
    string result = stringReplace (source, toReplace, replaceWith);
    string expected = "1234abcd8901234abcd8901234abcd890";

    bool pass = (0 == result.compare(expected));
    addTestResult("567", pass);


    source = "123456789012345678901234567890";
    toReplace = "123";
    replaceWith = "-";
    result = stringReplace(source, toReplace, replaceWith);
    expected = "-4567890-4567890-4567890";

    pass = (0 == result.compare(expected));
    addTestResult("start", pass);


    source = "123456789012345678901234567890";
    toReplace = "0";
    replaceWith = "";
    result = stringReplace(source, toReplace, replaceWith);
    expected = "123456789123456789123456789"; 

    pass = (0 == result.compare(expected));
    addTestResult("end", pass);


    source = "123123456789012345678901234567890";
    toReplace = "123";
    replaceWith = "-";
    result = stringReplace(source, toReplace, replaceWith);
    expected = "--4567890-4567890-4567890";

    pass = (0 == result.compare(expected));
    addTestResult("concat", pass);


    source = "1232323323123456789012345678901234567890";
    toReplace = "323";
    replaceWith = "-";
    result = stringReplace(source, toReplace, replaceWith);
    expected = "12-23-123456789012345678901234567890";

    pass = (0 == result.compare(expected));
    addTestResult("interleaved", pass);



    source = "1232323323123456789012345678901234567890";
    toReplace = "===";
    replaceWith = "-";
    result = utils_stringReplace(source, toReplace, replaceWith);
    expected = source;

    pass = (0 == result.compare(expected));
    addTestResult("no match", pass);

}

User · Answer

There is no one built-in function in C   to do this   If you d like to replace all instances of one substring with another  you can do so by intermixing calls to string  find and string  replace   For example   size t index   0  while  true            Locate the substring to replace          index   str find  abc   index        if  index    std  string  npos  break           Make the replacement          str replace index  3   def             Advance index forward so the next iteration doesn t pick it up as well          index    3      In the last line of this code  I ve incremented index by the length of the string that s been inserted into the string  In this particular example - replacing  abc  with  def  - this is not actually necessary  However  in a more general setting  it is important to skip over the string that s just been replaced  For example  if you want to replace  abc  with  abcabc   without skipping over the newly-replaced string segment  this code would continuously replace parts of the newly-replaced strings until memory was exhausted  Independently  it might be slightly faster to skip past those new characters anyway  since doing so saves some time and effort by the string  find function   Hope this helps

User · Answer

using std  string   string string replace  string src  string const amp  target  string const amp  repl           handle error situations trivial cases      if  target length      0               searching for a match to the empty string will result in              an infinite loop             it might make sense to throw an exception for this case         return src             if  src length      0            return src      nothing to match against            size t idx   0       for                idx   src find  target  idx           if  idx    string  npos   break           src replace  idx  target length    repl           idx    repl length               return src      Since it s not a member of the string class  it doesn t allow quite as nice a syntax as in your example  but the following will do the equivalent   test   string replace  string replace  test   abc    hij     def    klm

User · Answer

std  string replace std  string str  std  string substr1  std  string substr2        for  size t index   str find substr1  0   index    std  string  npos  amp  amp  substr1 length    index   str find substr1  index   substr2 length               str replace index  substr1 length    substr2       return str      Short solution where you don t need any extra Libraries

User · Answer

I think all solutions will fail if the length of the replacing string is different from the length of the string to be replaced   search for  abc  and replace by  xxxxxx   A general approach might be   void replaceAll  string  amp s  const string  amp search  const string  amp replace         for  size t pos   0    pos    replace length                  Locate the substring to replace         pos   s find  search  pos            if  pos    string  npos   break             Replace by erasing and inserting         s erase  pos  search length              s insert  pos  replace

User · Answer

std  string replace std  string str  const std  string amp  sub1  const std  string amp  sub2        if  sub1 empty            return str       std  size t pos      while   pos   str find sub1      std  string  npos          str replace pos  sub1 size    sub2        return str

User · Answer

string  amp  replace string  amp  subj  string old  string neu                size t uiui   subj find old           if  uiui    string  npos                       subj erase uiui  old size                subj insert uiui  neu                     return subj          I think this fits your requirement with few code

User · Answer

Replacing substrings should not be that hard   std  string ReplaceString std  string subject  const std  string amp  search                            const std  string amp  replace        size t pos   0      while  pos   subject find search  pos      std  string  npos             subject replace pos  search length    replace            pos    replace length              return subject      If you need performance  here is an optimized function that modifies the input string  it does not create a copy of the string   void ReplaceStringInPlace std  string amp  subject  const std  string amp  search                            const std  string amp  replace        size t pos   0      while  pos   subject find search  pos      std  string  npos             subject replace pos  search length    replace            pos    replace length              Tests   std  string input    abc abc def   std  cout  lt  lt   Input string     lt  lt  input  lt  lt  std  endl   std  cout  lt  lt   ReplaceString   return value                lt  lt  ReplaceString input   bc          lt  lt  std  endl  std  cout  lt  lt   ReplaceString   input string not changed                lt  lt  input  lt  lt  std  endl   ReplaceStringInPlace input   bc          std  cout  lt  lt   ReplaceStringInPlace   input string modified                lt  lt  input  lt  lt  std  endl    Output   Input string  abc abc def ReplaceString   return value  a   a   def ReplaceString   input string not modified  abc abc def ReplaceStringInPlace   input string modified  a   a   def

User · Answer

str replace str find str2  str2 length   str3     Where   str is the base string str2 is the sub string to find str3 is the replacement substring

User · Answer

Here is a solution using recursion that replaces all occurrences of a substring with another substring  This works no matter the size of the strings   std  string ReplaceString const std  string source string  const std  string old substring  const std  string new substring           Can t replace nothing      if  old substring empty            return source string          Find the first occurrence of the substring we want to replace      size t substring position   source string find old substring           If not found  there is nothing to replace      if  substring position    std  string  npos          return source string          Return the part of the source string until the first occurance of the old substring   the new replacement substring   the result of the same function on the remainder      return source string substr 0 substring position    new substring   ReplaceString source string substr substring position   old substring length   source string length   -  substring position   old substring length      old substring  new substring       Usage example   std  string my cpp string    This string is unmodified  You heard me right  it s unmodified    std  cout  lt  lt   The original C   string is  n   lt  lt  my cpp string  lt  lt  std  endl  my cpp string   ReplaceString my cpp string   unmodified    modified    std  cout  lt  lt   The final C   string is  n   lt  lt  my cpp string  lt  lt  std  endl

User · Answer

Generalizing on rotmax s answer  here is a full solution to search  amp  replace all instances in a string  If both substrings are of different size  the substring is replaced using string  erase and string  insert   otherwise the faster string  replace is used   void FindReplace string amp  line  string amp  oldString  string amp  newString      const size t oldSize   oldString length          do nothing if line is shorter than the string to find   if  oldSize  gt  line length     return     const size t newSize   newString length      for  size t pos   0    pos    newSize            Locate the substring to replace     pos   line find  oldString  pos        if  pos    string  npos   return      if  oldSize    newSize              if they re same size  use std  string  replace       line replace  pos  oldSize  newString          else            if not same size  replace by erasing and inserting       line erase  pos  oldSize          line insert  pos  newString

User · Answer

In c  11  you can use std  regex replace    include  lt string gt   include  lt regex gt   std  string test    abc def abc def   test   std  regex replace test  std  regex  def     klm

User · Answer

the impoved version by  Czarek Tomczak  allow both std  string and std  wstring   template  lt typename charType gt  void ReplaceSubstring std  basic string lt charType gt  amp  subject      const std  basic string lt charType gt  amp  search      const std  basic string lt charType gt  amp  replace        if  search empty      return        typename std  basic string lt charType gt   size type pos   0      while  pos   subject find search  pos      std  basic string lt charType gt   npos             subject replace pos  search length    replace            pos    replace length

User · Answer

std  string replace const std  string  amp  in                     const std  string  amp  from                     const std  string  amp  to     if from size      0   return in    std  string out         std  string tmp         for int i   0  ii   -1  i  lt  in size      i           change ii     if       ii  lt   0  amp  amp   from 0     in i             ii    0        tmp   from 0          else if  ii  gt   0  amp  amp  ii  lt  from size  -1            ii            tmp   tmp   in i         if from ii     in i             else           out   out   tmp          tmp               ii   -1                else         out   out   in i             if  tmp    from           out   out   to        tmp             ii   -1              return out

User · Answer

Boost String Algorithms Library way    include  lt boost algorithm string replace hpp gt        1     string test    abc def abc def     boost  replace all test   abc    hij      boost  replace all test   def    klm             2    string test   boost  replace all copy      boost  replace all copy lt string gt   abc def abc def    abc    hij         def        klm

User · Answer

If you are sure that the required substring is present in the string  then this will replace the first occurence of  abc  to  hij   test replace  test find  abc    3   hij      It will crash if you dont have  abc  in test  so use it with care

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