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i have an Vc++ application developed in VC6 . currently it supports 32 bit Operation systems. My requirement to covert this application to support 64 bit Operating systems (like windows7 , Windoes 2008 server and etc..).

what are easiest way / steps / procedure to migrate such of application?

+1  A: 

In practice, if you use every data type as it should, there shouldn't be a problem. Typical errors that are made, are:

  • using [unsigned] long instead of size_t when referring to sizes
  • subtracting pointers and assigning the result to a long (should be ptrdiff_t or something like this)
  • converting pointers to long or long to pointers

The page http://msdn.microsoft.com/en-us/library/aa384198%28v=VS.85%29.aspx on Microsoft's MSDN site gives a list of important things to think about when going to 64-bit.

Hope this helps.

Patrick
For a 32 bit application to work on 64 bit OS do we need to compile our source using 64 bit compiler?
coolcake
Visual Studio 2010 has a command file that sets the necessary environment variables for your compilation. Look for VCVARSALL.BAT. Execute this in a command prompt and give it the wanted 'type of compilation'. E.g. "VSVARSALL X86" sets everything ready for 32-bit compilations. "VSVARSALL X64" sets everything ready for 64-bit compilations.
Patrick