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c++ctype-conversionboolean

Is bool guaranteed to be 0 or 1 when converted to int?

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?
Solution

  • Yes:

    In 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.

    In C, when a value is converted to _Bool, it becomes 0 or 1 (§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.

    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).