Prevenir bufferoverflow scanf

while ( scanf("%20s", buf) == 1 ){

int scanner(const char *data, char *buffer, size_t buflen)
{
    char format[32];
    if (buflen == 0)
        return 0;
    snprintf(format, sizeof(format), "%%%ds", (int)(buflen-1));
    return sscanf(data, format, buffer);
}

gcc letssee.c -o letssee -fno-stack-protector