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# __w64
(Microsoft Specific) This keyword is obsolete. In versions of Visual Studio earlier than Visual Studio 2013, this lets you mark variables, so that when you compile with [/Wp64](../build/reference/wp64-detect-64-bit-portability-issues.md) the compiler will report any warnings that would be reported if you were compiling with a 64-bit compiler.  
  
## Syntax  
  
```  
  
type __w64 identifier  
```  
  
#### Parameters  
 `type`  
 One of the three types that could 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  
  
> [!IMPORTANT]
>  The [/Wp64](../build/reference/wp64-detect-64-bit-portability-issues.md) compiler option and `__w64` keyword are deprecated in Visual Studio 2010 and Visual Studio 2013 and removed starting in Visual Studio 2013. If you use the `/Wp64` compiler option on the command line, the compiler issues [Command-Line Warning D9002](http://msdn.microsoft.com/en-us/c58b405b-0f26-434e-b57f-4f05e1ca81e6). The `__w64` keyword is silently ignored. 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 [Configuring Programs for 64-Bit](../build/configuring-programs-for-64-bit-visual-cpp.md).  
  
 Any typedef that has `__w64` on it must be 32 bits on x86 and 64 bits on x64.  
  
 To detect portability issues by using versions of the Visual C++ compiler earlier than Visual Studio 2010, the `__w64` keyword should be specified on any typedefs that change size between 32 bit and 64 bit platforms. For any such type, `__w64` must 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](../build/reference/compiler-options.md)  
  
-   [Porting 32-Bit Code to 64-Bit Code](../build/common-visual-cpp-64-bit-migration-issues.md)  
  
-   [Configuring Programs for 64-Bit](../build/configuring-programs-for-64-bit-visual-cpp.md)  
  
## Example  
  
```  
// __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  
 [Keywords](../cpp/keywords-cpp.md)