Because in C character constants, such as ‘a’ have the type int. There’s a C FAQ about this suject: Perhaps surprisingly, character constants in C are of type int, so sizeof(‘a’) is sizeof(int) (though this is another area where C++ differs).
Is my usage of assert as the left operand of the comma expression valid standard C? That is, does the standard allow me to use assert as an expression? Yes, it is valid as the left operand of the comma operator can be an expression of type void. And assert function has void as its … Read more
sizeof returns size_t you need to use %zu for the format string instead of %d. The type of unsigned integer of size_t can vary (depending on platform) and may not be long unsigned int everywhere, which is covered in the draft C99 standard section 6.5.3.4 The sizeof operator paragraph 4: The value of the result … Read more
The class contains no data members, so it’s empty. The standard demands that every class have at least size 1, so that’s what you get. (Member functions aren’t physically “inside” a class, they’re really just free functions with a hidden argument and a namespace and access control.)
Yes, this causes undefined behaviour. In N1570 6.5.3.4/2 we have: The sizeof operator yields the size (in bytes) of its operand, which may be an expression or the parenthesized name of a type. The size is determined from the type of the operand. The result is an integer. If the type of the operand is … Read more
size_t is defined by the C standard to be the unsigned integer return type of the sizeof operator (C99 6.3.5.4.4), and the argument of malloc and friends (C99 7.20.3.3 etc). The actual range is set such that the maximum (SIZE_MAX) is at least 65535 (C99 7.18.3.2). However, this doesn’t let us determine sizeof(size_t). The implementation … Read more
It’s actually quite common to store a number without needing to know the exact size of the type. There are plenty of quantities in my programs that I can reasonably assume won’t exceed 2 billion, or enforce that they don’t. But that doesn’t mean I need an exact 32 bit type to store them, any … Read more
This is a C++ interview test question not homework. Then your interviewer needs to refresh his recollection with how the C++ standard works. And I quote: For an enumeration whose underlying type is not fixed, the underlying type is an integral type that can represent all the enumerator values defined in the enumeration. The whole … Read more
The following could be ambiguous: sizeof int * + 1 Is that (sizeof (int*)) + 1, or (sizeof(int)) * (+1)? Obviously the C language could have introduced a rule to resolve the ambiguity, but I can imagine why it didn’t bother. With the language as it stands, a type specifier never appears “naked” in an … Read more
What you are trying to do is not possible to do in any elegant way. It is not possible to reliably access consecutive struct members as an array. The currently accepted answer is a hack, not a solution. The proper solution would be to switch to an array, regardless of how much work it is … Read more