What is the Size of `sizeof(bool)` According to the C Standard?

Sizeof(bool) in the C Language Standard

The size of a bool variable in C , expressed by sizeof(bool), is a subject of ongoing discussion within the programming community. This article delves into the C language standard to determine the exact specification for sizeof(bool) and resolves the uncertainty surrounding its implementation.

Standard Specification

The C language standard, in Section 5.3.3/1, clearly states that the size of fundamental types other than char, signed char, and unsigned char is implementation-defined. This includes bool and wchar_t. Specifically, the standard notes that sizeof(bool) does not have to be equal to 1.

Implementation Implications

The implementation-defined nature of sizeof(bool) allows compilers and platforms to optimize the size of bool variables based on their specific design and constraints. This flexibility gives implementers the freedom to balance space efficiency with performance considerations. As a result, the size of a bool can vary across different compilers and hardware architectures.

Practical Implications

In practice, most modern C implementations represent bool values using a single bit (8 bytes). However, there have been exceptions in the past where bool occupied a larger memory footprint. For example, some early Macintosh compilers used 16 bits for bool, while certain embedded systems may use even larger representations.

Conclusion

The C language standard does not specify the size of bool as part of its core requirements. Instead, it leaves the implementation of sizeof(bool) up to the discretion of individual compilers and platforms. This flexibility allows for efficient and tailored optimizations in various computing environments while maintaining compatibility with the C specification.

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