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Microsoft Specific

type __w64 identifier


One of the three types that might cause problems in code being ported from a 32-bit to a 64-bit compiler: int, long, or a pointer.
The identifier for the variable you are creating.


The __w64 keyword lets you mark variables, such that when you compile with /Wp64 the compiler will report any warnings that would be reported if you were compiling with a 64-bit compiler.

Any typedef that has __w64 on it must be 32 bits on x86 and 64 bits on ia64.

The __w64 modifier should be specified on any typedefs that change size between 32 bit and 64 bit platforms. For any such type, __w64 should appear only on the 32-bit definition of the typedef. For example:

#ifdef  _WIN64
typedef unsigned __int64    size_t;
typedef _W64 unsigned int   size_t;

__w64 is ignored if the compilation does not use /Wp64.


// __w64.cpp
// compile with: /W3 /Wp64
typedef int Int_32;
#ifdef _WIN64
typedef __int64 Int_Native;
typedef int __w64 Int_Native;

int main()
   Int_32 i0 = 5;
   Int_Native i1 = 10;
   i0 = i1;   // C4244 64-bit int assigned to 32-bit int

   // char __w64 c;  error, cannot use __w64 on char

END Microsoft Specific

See Also

C++ Keywords