bool から int への変換は 0 または 1 であることが保証されていますか?

bool Conversion to int: Guaranteed to be 0 or 1?

Question:

Many compilers appear to store bool values as either 0 or 1, but is this behavior guaranteed? Specifically, in the following snippet:

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

Answer:

Yes, bool values are guaranteed to be converted to either 0 or 1 when converted to int. This behavior is defined in both the C++ and C standards:

C++ (§4.5/4):

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

C (§6.3.1.2/1):

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

Therefore, in the given example, b will be converted to either 0 (if a is not equal to 0) or 1 (if a is equal to 0). Adding 3 to b will result in either 4 or 5, depending on the value of a.

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