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.

Example

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.

See Also

VirtualAlloc Method
VirtualFree Method