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bool (C++)

This keyword is a built-in type. A variable of this type can have values true and false. Conditional expressions have the type bool and so have values of type bool. For example, i!=0 now has true or false depending on the value of i.

The values true and false have the following relationship:

!false == true
!true == false

In the following statement:

if (condexpr1) statement1; 

If condexpr1 is true, statement1 is always executed; if condexpr1 is false, statement1 is never executed.

When a postfix or prefix ++ operator is applied to a variable of type bool, the variable is set to true. The postfix or prefix -- operator cannot be applied to a variable of this type.

The bool type participates in integral promotions. An r-value of type bool can be converted to an r-value of type int, with false becoming zero and true becoming one. As a distinct type, bool participates in overload resolution.

In Visual C++4.2, the Standard C++ header files contained a typedef that equated bool with int. In Visual C++ 5.0 and later, bool is implemented as a built-in type with a size of 1 byte. That means that for Visual C++ 4.2, a call of sizeof(bool) yields 4, while in Visual C++ 5.0 and later, the same call yields 1. This can cause memory corruption problems if you have defined structure members of type bool in Visual C++ 4.2 and are mixing object files (OBJ) and/or DLLs built with the 4.2 and 5.0 or later compilers.

The __BOOL_DEFINED macro can be used to wrap code that is dependent on whether or not bool is supported.

// bool.cpp
#include <stdio.h>

int main()
{
    #if !defined(__BOOL_DEFINED)
        printf_s("bool is not supported\n");
    #elif defined(__BOOL_DEFINED)
    printf_s("bool is supported\n");
    #endif
}

Output

bool is supported

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