当类型转换为 int 时,C/C++ bool 类型是否总是保证为 0 或 1?

2022-01-19 00:00:00 c boolean c++

许多编译器似乎只在 bool 值中保留 0 或 1,但我不确定这是否总是有效:

Many compilers seem to be keeping only 0 or 1 in bool values, but I'm not sure this will always work:

int a = 2;
bool b = a;
int c = 3 + b; // 4 or 5?

推荐答案

是的:

在 C++ 中(第 4.5/4 节):

In C++ (§4.5/4):

bool 类型的右值可以是转换为 int 类型的右值,假变成零和真合而为一.

An rvalue of type bool can be converted to an rvalue of type int, with false becoming zero and true becoming one.

在 C 中,当一个值转换为 _Bool 时,它变为 0 或 1(第 6.3.1.2/1 节):

In C, when a value is converted to _Bool, it becomes 0 or 1 (§6.3.1.2/1):

当任何标量值转换为_Bool,如果值比较等于0,则结果为0;否则,结果是 1.

When any scalar value is converted to _Bool, the result is 0 if the value compares equal to 0; otherwise, the result is 1.

当转换为 int 时,它非常简单.int 可以容纳 0 和 1,因此值没有变化(第 6.3.1.3 节).

When converting to int, it's pretty straight-forward. int can hold 0 and 1, so there's no change in value (§6.3.1.3).

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