size guarantee for integral/arithmetic types in C and C++

Question

I know that the C++ standard explicitly guarantees the size of only char, signed char and unsigned char. Also it gives guarantees that

Answer 1

There are several inaccuracies in what you read. These inaccuracies were either present in the source, or maybe you remembered it all incorrectly.

Firstly, a pedantic remark about one peculiar difference between C and C++. C language does not make any guarantees about the relative sizes of integer types (in bytes). C language only makes guarantees about their relative ranges. It is true that the range of int is always at least as large as the range of short and so on. However, it is formally allowed by C standard to have sizeof(short) > sizeof(int). In such case the extra bits in short would serve as padding bits, not used for value representation. Obviously, this is something that is merely allowed by the legal language in the standard, not something anyone is likely to encounter in practice.

In C++ on the other hand, the language specification makes guarantees about both the relative ranges and relative sizes of the types, so in C++ in addition to the above range relationship inherited from C it is guaranteed that sizeof(int) is greater or equal than sizeof(short).

Secondly, the C language standard guarantees minimum range for each integer type (these guarantees are present in both C and C++). Knowing the minimum range for the given type, you can always say how many value-forming bits this type is required to have (as minimum number of bits). For example, it is true that type long is required to have at least 32 value-forming bits in order to satisfy its range requirements. If you want to recalculate that into bytes, it will depend on what you understand under the term byte. If you are talking specifically about 8-bit bytes, then indeed type long will always consist of at least four 8-bit bytes. However, that does not mean that sizeof(long) is always at least 4, since in C/C++ terminology the term byte refers to char objects. char objects are not limited to 8-bits. It is quite possible to have 32-bit char type in some implementation, meaning that sizeof(long) in C/C++ bytes can legally be 1, for example.