Is sizeof(bool) defined?

问题:

I can\'t find an answer in the standard documentation. Is sizeof(bool) always 1-byte, or is it implementation defined?

回答1:

It\'s implementation defined, and the standard puts notable emphasis on making that clear.

§5.3.3/1, abridged:

sizeof(char), sizeof(signed char) and sizeof(unsigned char) are 1; the result of sizeof applied to any other fundamental type is implementation-defined. [Note: in particular, sizeof(bool) and sizeof(wchar_t) are implementation-defined.⁶⁹⁾]

Footnote 69):

sizeof(bool) is not required to be 1.

回答2:

http://msdn.microsoft.com/en-us/library/tf4dy80a.aspx

\"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.\"

回答3:

It\'s implementation defined. Only sizeof(char) is 1 by the standard.

回答4:

See 5.3.3 paragraph 1 :

[Note: in particular, sizeof(bool) and sizeof(wchar_t) are implementation-defined.69) ]