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:

• MSVC Compiler Options

• Migration Tips

See also

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