Question

Size of char, signed char and unsigned char is defined to be 1 byte, by the C++ Standard itself. I’m wondering why it didn’t define the sizeof(bool) also?

C++03 Standard $5.3.3/1 says,

sizeof(char), sizeof(signed char) and
sizeof(unsigned char) are 1; the
result of sizeof applied to any other
fundamental type (3.9.1) is
implementation-defined. [Note: in
particular,sizeof(bool) and
sizeof(wchar_t) are
implementation-defined.69)

I understand the rationale that sizeof(bool) cannot be less than one byte. But is there any rationale why it should be greater than 1 byte either? I’m not saying that implementations define it to be greater than 1, but the Standard left it to be defined by implementation as if it may be greater than 1.

If there is no reason sizeof(bool) to be greater than 1, then I don’t understand why the Standard didn’t define it as just 1 byte, as it has defined sizeof(char), and it’s all variants.

Answer 1

Many platforms cannot effectively load values smaller than 32 bits. They have to load 32 bits, and use a shift-and-mask operation to extract 8 bits. You wouldn’t want this for single bools, but it’s OK for strings.