how to replace substring in c?

Question

This example works but I think that the memory leaks. Function used in the simple web server module and thus shared memory grows if you use this function.

Answer 1

One problem I can see is that if the replacement string contains the search string, you'll loop forever (until you run out of memory).

For example:

char *result = str_replace("abc", "a", "aa");

Also, doing another malloc/free every time you replace one instance is pretty expensive.

A better approach would be to do exactly 2 passes over the input string:

• the first pass, count how many instances of the search string are present

• now that you know how many matches, compute the length of your result & malloc once:

  strlen(string) + matches*(strlen(replacement)-strlen(substr)) + 1

• make a second pass through the source string, copying/replacing