Question

Should I free up memory returned by the following two functions in the caller function? I see that it is ok with function get_current_time but not ok with the get_filename_ext. I see similar question here, but not sure that answers my question. In general what should I look for?

char *get_current_time(void){
    struct tm *local;
    time_t t;
    t = time(NULL);
    local = gmtime(&t);
    return asctime(local);
}

char *get_filename_ext(const char *filename) {
        const char *dot = strrchr(filename, '.');
        if(!dot || dot == filename) return "";
        return dot + 1;
    }

Answer 1

Neither of these functions allocate any memory. So there’s actually nothing to free.

The char* returned by asctime is an internal buffer. So you can’t free it anyway.