# w64

\_\_w64 is a special key word of Visual C\+\+ compiler by which we should mark the types which will become 64\-bit when compiling the code on a 64\-bit system\. This allows Visual C\+\+ compiler to perform some preliminary code tests for compatibility with 64\-bit systems while it is built only in 32\-bit mode\. This diagnosis is performed if the key [Wp64](https://pvs-studio.com/en/blog/terms/0057/) is defined \(Detect 64\-Bit Portability Issues\)\.

## References

1. Andrey Karpov\. [64 bits, Wp64, Visual Studio 2008, Viva64 and all the rest](https://pvs-studio.com/en/blog/posts/cpp/a0021/)\.\.\.
1. MSDN\. [Microsoft Specific keyword \_\_w64](https://www.microsoft.com/en-us/download/details.aspx?id=55984)\.