std::string replace between start and end

As I see it, two checks are missing:

1. If endString is not found,
2. If endString is found before startString, in this case, your substraction to compute the second parameter of replace() will result in a negative length which will overflow.

Also, you might want to return a boolean to check whether there was a match or not.

Try something like this instead:

static bool replaceString(string &input, const string &startString, const string &endString, const string &replacement) { size_t indexStart, indexEnd; indexStart = input.find(startString); if (indexStart == input.npos) { return false; } indexEnd = input.find(endString, indexStart); // Note the offset to start searching // after the start index if (indexEnd == input.npos) { return false; } input.replace(indexStart, indexEnd-indexStart, replacement); return true; } 

Test program:

int main (int, char**) { string s ("abcdefghijklmnopqrstuvwxyz"); string start ("gh"); string end ("pq"); string replace ("GHIJKLMNO"); bool ok = replaceString(s, start, end, replace); std::cout << "1. found? " << ok << ", result: " << s << std::endl; start = "pq"; end = "de"; ok = replaceString(s, start, end, replace); std::cout << "2. found? " << ok << ", result: " << s << std::endl; return 0; } 

Output:

1. found? true, result: abcdefGHIJKLMNOpqrstuvwxyz 2. found? false, result: abcdefGHIJKLMNOpqrstuvwxyz 

This answer is similar to Julien-L's but I think you also need to advance indexStart so the replacement doesn't overwrite any of the found startString.

static void replaceString(std::string &input, const std::string &startString, const std::string &endString, const std::string &replacement) { size_t indexStart = input.find(startString); if (indexStart == input.npos) return; indexStart += startString.size(); size_t indexEnd = input.find(endString, indexStart); if (indexEnd == input.npos) return; input.replace(indexStart, indexEnd - indexStart, replacement); }