Thread: Replacing part of a string?

Your idea works, but you don't really need firstpart and secondpart as you can write directly to fullstring. Here's my example:

Code:

/* Interpolate src by substituting placeholder with the decimal string
 * representation of value, writing the result, including the terminating null
 * character, to the first n chars of dest, returning dest.
 */
char *interpolate(char *dest,
                  size_t n,
                  const char *src,
                  const char *placeholder,
                  int value)
{
    if (n > 0)
    {
        char *p = strstr(src, placeholder);
        if (p)
        {
            size_t first_segment_len = (size_t)(p - src);
            if (first_segment_len >= n)
            {
                first_segment_len = n - 1;
            }
            dest[0] = '\0';
            strncat(dest, src, first_segment_len);
            snprintf(dest + first_segment_len,
                     n - first_segment_len,
                     "%d%s",
                     value,
                     p + strlen(placeholder));
        }
        else
        {
            dest[0] = '\0';
            strncat(dest, src, n - 1);
        }
    }
    return dest;
}

Applying the above to your example, you would call interpolate like this:

Code:

interpolate(fullstring, MAX_LEN, "hello$$hello", "$$", 123);