strncat

char *strncat(char *dest, const char *src, size_t n)

char *strncat(char *dest, const char *src, size_t n)
{
    char *ret = dest;
    while (*dest)
        dest++;
    while (n--)
        if (!(*dest++ = *src++))
            return ret;
    *dest = 0;
    return ret;
}