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GCC Switch Fallthrough Warning

GCC 7 之後多了一個新的 warning 選項, -Wimplicit-fallthrough, 檢查 switch 中的每個 case 的最後一個 statement 是否為 break 或 return. 若程式邏輯需要 fall through 的話, 需要加特殊的註解, 來避免 GCC 產生 warning,

C or C++ (before C++17)

加入 /* fallthrough */, /* FALLTHRU */, __attribute__ ((fallthrough));.

switch (c) {
	case 0:
		foo();
		break;
	case 1:
		bar(1);
		__attribute__ ((fallthrough));
	case 2:
		bar(2);
		/* FALLTHRU */
	case 3:
		bar(-1);
		break;
}

C++17

可以使用 [[fallthrough]];

switch (c) {
	case 0:
		foo();
		[[fallthrough]];
	case 3:
		bar();
		break;
}

Reference

C CPP Written on October 2nd , 2021 by Borting
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