c macro 將參數從數字轉成字串

#define str(s) #s

int main(void)
{
str("tt")
return 0;
}

descent@ubuntu:test$ gcc -E v.c
# 1 "v.c"
# 1 ""
# 1 ""
# 1 "v.c"



int main(void) {
"\"tt\""
return 0;
}

---

#define str(s) #s

int main(void)
{
str(1)
return 0;
}

descent@ubuntu:test$ gcc -E v.c
# 1 "v.c"
# 1 ""
# 1 ""
# 1 "v.c"

#define str(s) #s

int main(void)
{
"1";
return 0;
}

不知道是 GNU extension 還是標準用法？