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Important This document may not represent best practices for current development, links to downloads and other resources may no longer be valid. Current recommended version can be found here.

Common Visual C++ 64-bit Migration Issues 

When you use Visual C++ 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 C++ versions before Visual C++ 2005. In Visual C++ 2005 and later, time_t is 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 an integer on a Windows 32-bit operating system.

  • Use %I64x to display an integer on a Windows 64-bit operating system.

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

For more information, see:

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