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GCC拡張で式指向にbreakとかcontinueとか

Last updated at Posted at 2024-11-01

ZigとかRustみたいに式の中でbreakとかcontinueするマクロ

#define break ({ break; 0; })
#define continue ({ continue; 0; })

void test() {
  for (;;) {
    int a = break;
    // unreachable
  }
  for (int i = 0; i < 5; i++) {
    if (continue) {}
    // unreachable
  }
}

nullチェックみたいな使い方ができる

#define break ({ break; (void *)0; })
#define continue ({ continue; (void *)0 })
#define orelse ?:

void test() {
  for (...) {
    char *p = malloc(100) orelse break;
    ...
  }
}

いちおう文としても書ける

#define break ({ break; 0; })

void test() {
  for (;;) {
    break;
  }
}

returnは括弧が必要になる(ださい)

#define return(x) ({ return x; (void *)0; })
#define orelse ?:

int test() {
  char *p = malloc(100) orelse return(1);
  ...
}
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