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C6333

warning C6333: Invalid parameter: passing MEM_RELEASE and a non-zero dwSize parameter to <function> is not allowed. This results in the failure of this call

This warning indicates an invalid parameter is being passed to VirtualFree or VirtualFreeEx. Both of these functions reject a dwFreeType of MEM_RELEASE with a non-zero value of dwSize. When passing MEM_RELEASE, the dwSize parameter must be zero. Also, make sure that the return value of this function is not ignored.

The following sample code generates this warning:

#include <windows.h>
#define PAGELIMIT 80            

DWORD dwPages = 0;  // count of pages 
DWORD dwPageSize;   // page size 

VOID f( VOID )
{
  LPVOID lpvBase;            // base address of the test memory
  BOOL bSuccess;           
  SYSTEM_INFO sSysInfo;      // system information

  GetSystemInfo( &sSysInfo );  
  dwPageSize = sSysInfo.dwPageSize;

  // Reserve pages in the process's virtual address space
  lpvBase = VirtualAlloc(
                         NULL,                // system selects address
                         PAGELIMIT*dwPageSize,// size of allocation
                         MEM_RESERVE,        
                         PAGE_NOACCESS );     
  if (lpvBase)
  {
    // code to access memory 
  }
  else
  {
    return;
  }

  bSuccess = VirtualFree(lpvBase, PAGELIMIT * dwPageSize, MEM_RELEASE); 
  //code...
}

To correct this warning, use the following sample code:

#include <windows.h>
#define PAGELIMIT 80            

DWORD dwPages = 0;  // count of pages 
DWORD dwPageSize;   // page size 

VOID f( VOID )
{
  LPVOID lpvBase;            // base address of the test memory
  BOOL bSuccess;           
  SYSTEM_INFO sSysInfo;      // system information

  GetSystemInfo( &sSysInfo );  
  dwPageSize = sSysInfo.dwPageSize;

  // Reserve pages in the process's virtual address space
  lpvBase = VirtualAlloc(
                         NULL,                // system selects address
                         PAGELIMIT*dwPageSize,// size of allocation
                         MEM_RESERVE,        
                         PAGE_NOACCESS );     
  if (lpvBase)
  {
    // code to access memory 
  }
  else
  {
    return;
  }
  bSuccess = VirtualFree(lpvBase, 0, MEM_RELEASE );

  //  VirtualFree(lpvBase, PAGELIMIT * dwPageSize, MEM_DECOMMIT); 
  // code...
}

You can also use VirtualFree(lpvBase, PAGELIMIT * dwPageSize, MEM_DECOMMIT); call to decommit pages, and later release them using MEM_RELEASE flag.

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