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Visual C++ 10 is shipped with stdlib.h that among other things contains this gem:
template <typename _CountofType, size_t _SizeOfArray>
char (*__countof_helper(UNALIGNED _CountofType (&_Array)[_SizeOfArray]))[_SizeOfArray];
#define _countof(_Array) (sizeof(*__countof_helper(_Array)) + 0)
which uses a clever template trick to deduce array size and prevent pointers from being passed into __countof.
What’s the purpose of + 0 in the macro definition? What problem does it solve?
Quoting STL from here