Is sizeof(bool) defined in the C++ language standard?

Question

I can't find an answer in the standard documentation. Does the C++ language standard require sizeof(bool) to always be 1 (for 1 byte), or is this size implementation-defined?

GManNickG · Accepted Answer · 2019-01-31T00:15:06.877

187

sizeof(bool) is implementation defined, and the standard puts notable emphasis on this fact.

§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.

edited Jan 31 '19 at 00:15

answered Feb 04 '11 at 12:16

GManNickG

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is there a flag that i need to compile my program with, that my compiler will use only 1 byte for `bool`? – Eagle May 30 '11 at 09:29
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@Eagle: That's up to your compiler, I'm not sure. It's probably best you left it up to your compiler. – GManNickG May 30 '11 at 10:02
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note that std::vector is optimized to a vector containing 1bit bools by the standard. – user3063349 Feb 10 '16 at 16:40
@user3063349 Any reference? – John Sep 05 '21 at 02:24
@user3063349 is it standard really? [This](https://en.cppreference.com/w/cpp/container/vector_bool) mentions implementation-dependence – Szymon Brych Jan 07 '22 at 07:57

score 20 · Answer 2 · answered Aug 04 '11 at 01:50

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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."

answered Aug 04 '11 at 01:50

Yi Ling

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You do realize that this is somewhat related to the question, but clearly not an answer, since 0xbadf00d asked about the standard, not some specific/arbitrarily selected compiler implementation, right? – Christopher Creutzig Dec 12 '13 at 22:27
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@ChristopherCreutzig It is a proof by counterexample. – kinokijuf May 24 '14 at 20:50
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@kinokijuf It's not a counterexample. There are many things in Visual C++ that are not standard-compliant. – 0xbadf00d May 13 '16 at 15:43

score 11 · Answer 3 · answered Feb 04 '11 at 12:16

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

answered Feb 04 '11 at 12:16

peoro

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pls note that the 1 in the standard can mean 4 byte. Than every type is a product of 4. So care that the standard ONLY defines char is the 1, but not defines the measurment. – user3063349 Feb 10 '16 at 16:39
1 means 8 bits or 1 byte in the standard – paulm Jul 01 '16 at 11:41
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1 byte. The number of bits per byte is not defined by the standard (it needs to be at least 8 IIRC), but can be found in `CHAR_BIT`, defined in `climits`. – peoro Jul 02 '16 at 02:13

score 3 · Answer 4 · answered Feb 04 '11 at 12:19

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See 5.3.3 paragraph 1 :

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

answered Feb 04 '11 at 12:19

BЈовић

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Is sizeof(bool) defined in the C++ language standard?

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