C++ ArraySize Macros

C++ ArraySize Macros

VC stdlib.h macro

/* _countof helper */
#if !defined(_countof)
#if !defined(__cplusplus)
#define _countof(_Array) (sizeof(_Array) / sizeof(_Array[0]))
#else
extern "C++"
{
template <typename _CountofType, size_t _SizeOfArray>
char (*__countof_helper(UNALIGNED _CountofType (&_Array)[_SizeOfArray]))[_SizeOfArray];
#define _countof(_Array) (sizeof(*__countof_helper(_Array)) + 0)
}
#endif
#endif

============================
Pasted from <http://blogs.msdn.com/b/the1/archive/2004/05/07/128242.aspx> 

template <typename T, size_t N>
char ( &_ArraySizeHelper( T (&array)[N] ))[N];
 
#define countof( array ) (sizeof( _ArraySizeHelper( array ) ))

=====================
http://code.google.com/p/protobuf/source/browse/trunk/src/google/protobuf/stubs/common.h

// ===================================================================
// from google3/base/basictypes.h

// The GOOGLE_ARRAYSIZE(arr) macro returns the # of elements in an array arr.
// The expression is a compile-time constant, and therefore can be
// used in defining new arrays, for example.
//
// GOOGLE_ARRAYSIZE catches a few type errors.  If you see a compiler error
//
//   "warning: division by zero in ..."
//
// when using GOOGLE_ARRAYSIZE, you are (wrongfully) giving it a pointer.
// You should only use GOOGLE_ARRAYSIZE on statically allocated arrays.
//
// The following comments are on the implementation details, and can
// be ignored by the users.
//
// ARRAYSIZE(arr) works by inspecting sizeof(arr) (the # of bytes in
// the array) and sizeof(*(arr)) (the # of bytes in one array
// element).  If the former is divisible by the latter, perhaps arr is
// indeed an array, in which case the division result is the # of
// elements in the array.  Otherwise, arr cannot possibly be an array,
// and we generate a compiler error to prevent the code from
// compiling.
//
// Since the size of bool is implementation-defined, we need to cast
// !(sizeof(a) & sizeof(*(a))) to size_t in order to ensure the final
// result has type size_t.
//
// This macro is not perfect as it wrongfully accepts certain
// pointers, namely where the pointer size is divisible by the pointee
// size.  Since all our code has to go through a 32-bit compiler,
// where a pointer is 4 bytes, this means all pointers to a type whose
// size is 3 or greater than 4 will be (righteously) rejected.
//
// Kudos to Jorg Brown for this simple and elegant implementation.

#undef GOOGLE_ARRAYSIZE
#define GOOGLE_ARRAYSIZE(a) \
  ((sizeof(a) / sizeof(*(a))) / \

   static_cast<size_t>(!(sizeof(a) % sizeof(*(a)))))