How to Replace Arbitrary Text in String in C++

The C++ string library has several useful functions for manipulating strings, but no general search and replace. Although there is a lot of information on optimized algorithms for implementing arbitrary text replacement, many algorithms involve complex data structures and hard-to-follow techniques such as pointer arithmetic. For most programs, search and replace isn't a performance bottleneck, so it makes more sense to use a simple, easily understandable algorithm. This is possible by taking advantage of some of the existing string functions to handle the low-level manipulation.

Instructions

1. Write the outline of your string replacement function:

   string replaceSubstring(string source, string match, string replace)
   {
   string out = "";
   return out;
   }

2. Add a loop that finds all substring matches in the string. The variable lastpos will be helpful when you start adding the code to build the new string:

   size_t pos = 0; //Start searching at the first character
   size_t lastpos = 0;
   while((pos = source.find(match, pos)) != string::npos) //loop until no matches are found
   {
   pos = pos + match.lengh(); //Start the search for the next match at the end of this match
   lastpos = pos;
   }

3. Build the output string as matches are found:

   size_t pos = 0; //Start searching at the first character
   size_t lastpos = 0;
   while((pos = source.find(match, pos)) != string::npos) //loop until no matches are found
   {
   output += source.substr(lastpos, pos - lastpos); //Add all characters that were skipped over
   output += replace;
   pos = pos + match.lengh(); //Start the search for the next match at the end of this match
   lastpos = pos;
   }
   output += source.substr(lastpos); //Add the remainder of the source string

References

• Cplusplus.com C++: String