一个奇怪的问题

#include "stdafx.h"
#include <wtypes.h>
#include <iostream>

using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
 PVOID pvResult = NULL;
 pvResult = VirtualAlloc(NULL, 8*1024, MEM_RESERVE|MEM_TOP_DOWN, PAGE_READWRITE);
 int aa = (int)pvResult;
 printf("%x", aa);
 
 PVOID pvRel = VirtualAlloc(pvResult, 6*1024, MEM_COMMIT, PAGE_READWRITE);
 
 BOOL bValue = VirtualFree(pvRel, 0, MEM_DECOMMIT|MEM_RELEASE);

 int* pVal = (int*)pvResult;
 *pVal = 2;

 getchar();
 return 0;
}

此段代码竟然能运行成功, 没发生任何异常. 奇怪!!!