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common-visual-cpp-64-bit-migration-issues.md

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description title ms.date helpviewer_keywords ms.assetid
Learn more about: Common Visual C++ 64-bit Migration Issues
Common Visual C++ 64-bit Migration Issues
05/06/2019
64-bit programming [C++], migration
64-bit compiler [C++], migration
porting 32-bit code to 64-bit code
migration [C++], 64-bit code issues
32-bit code porting [C++]
64-bit applications [C++]
64-bit compiler [C++], porting 32-bit code
Win64 [C++]
d17fb838-7513-4e2d-8b27-a1666f17ad76

Common Visual C++ 64-bit Migration Issues

When you use the Microsoft C++ compiler (MSVC) to create applications to run on a 64-bit Windows operating system, you should be aware of the following issues:

  • An int and a long are 32-bit values on 64-bit Windows operating systems. For programs that you plan to compile for 64-bit platforms, you should be careful not to assign pointers to 32-bit variables. Pointers are 64-bit on 64-bit platforms, and you will truncate the pointer value if you assign it to a 32-bit variable.

  • size_t, time_t, and ptrdiff_t are 64-bit values on 64-bit Windows operating systems.

  • time_t is a 32-bit value on 32-bit Windows operating systems in Visual Studio 2005 and earlier. time_t is now a 64-bit integer by default. For more information, see Time Management.

    You should be aware of where your code takes an int value and processes it as a size_t or time_t value. It is possible that the number could grow to be larger than a 32-bit number and data will be truncated when it is passed back to the int storage.

The %x (hex int format) printf modifier will not work as expected on a 64-bit Windows operating system. It will only operate on the first 32 bits of the value that is passed to it.

  • Use %I32x to display a 32-bit integral type in hex format.

  • Use %I64x to display a 64-bit integral type in hex format.

  • The %p (hex format for a pointer) will work as expected on a 64-bit Windows operating system.

For more information, see:

See also

Configure C++ projects for 64-bit, x64 targets
Visual C++ Porting and Upgrading Guide