__w64 copied from MSDN

__w64

Visual Studio 2010

 

 

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(Microsoft Specific) 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.

 

 

type __w64 identifier

Parameters

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type

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.

identifier

The identifier for the variable you are creating.

Remarks

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Important

The /Wp64 compiler option and __w64 keyword are deprecated and will be removed in a future version of the compiler. If you use the /Wp64 compiler option on the command line, the compiler issuesCommand-Line Warning D9035. Instead of using this option and keyword to detect 64-bit portability issues, use a Visual C++ compiler that targets a 64-bit platform. For more information, see 64-Bit Programming with Visual C++.

Any typedef that has __w64 on it must be 32 bits on x86 and 64 bits on Itanium Processor Family (IPF).

The __w64 keyword 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.

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

For more information about porting to 64-bit, see the following topics:

• Compiler Options

• /Wp64

• Porting 32-Bit Code to 64-Bit Code

• 64-Bit Programming with Visual C++

Example

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

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
}

See Also

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Reference

C++ Keywords