Check Windows 7 version in Visual C++

For MFC code, it's a little easier:

afxGlobalData.bIsWindows7

This variable will be set to true on Windows 7 and newer.

Consider using VerifyVersionInfo() to do requirements checking.
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Here is a sample pulled from MSDN:

#include <windows.h>
#include <stdio.h>

BOOL Is_WinXP_SP2_or_Later () 
{
   OSVERSIONINFOEX osvi;
   DWORDLONG dwlConditionMask = 0;
   int op=VER_GREATER_EQUAL;
 
   // Initialize the OSVERSIONINFOEX structure.

   ZeroMemory(&osvi, sizeof(OSVERSIONINFOEX));
   osvi.dwOSVersionInfoSize = sizeof(OSVERSIONINFOEX);
   osvi.dwMajorVersion = 5;
   osvi.dwMinorVersion = 1;
   osvi.wServicePackMajor = 2;
   osvi.wServicePackMinor = 0;
 
   // Initialize the condition mask.

   VER_SET_CONDITION( dwlConditionMask, VER_MAJORVERSION, op );
   VER_SET_CONDITION( dwlConditionMask, VER_MINORVERSION, op );
   VER_SET_CONDITION( dwlConditionMask, VER_SERVICEPACKMAJOR, op );
   VER_SET_CONDITION( dwlConditionMask, VER_SERVICEPACKMINOR, op );
 
   // Perform the test.

   return VerifyVersionInfo(
      &osvi, 
      VER_MAJORVERSION | VER_MINORVERSION | 
      VER_SERVICEPACKMAJOR | VER_SERVICEPACKMINOR,
      dwlConditionMask);
}
 
void main()
{
    if(Is_WinXP_SP2_or_Later())
        printf("The system meets the requirements.\n");
    else printf("The system does not meet the requirements.\n");
}

VerifyVersionInfo()