LPVOID WINAPI VirtualAlloc( __in LPVOID lpAddress, __in SIZE_T dwSize, __in DWORD flAllocationType, __in DWORD flProtect );在重置内存区域的时候，有两种可能：
- 当区域页面已经在分页文件中时，表示该页面已经被替换出去了。调用 VirtualAlloc 函数重置后，系统会直接删除对应的页面。
- 当区域页面还在RAM中时，调用 VirtualAlloc 函数重置后，页面都会被标记为"未修改"，这样它们被替换出去的时候就不会被写到分页文件中去了。
下面是《windows核心编程》中的一个示例：
#include系列文章是本人看《windows核心编程》时的一些学习笔记，有疏忽之处，欢迎各位网友指正。QQ邮箱：job.zhanghui@qq.com#include int WINAPI _tWinMain(HINSTANCE, HINSTANCE, PTSTR, int) { TCHAR szAppName[] = TEXT("MEM_RESET tester"); TCHAR szTestData[] = TEXT("Some text data"); // Commit a page of storage and modify its contents. PTSTR pszData = (PTSTR) VirtualAlloc(NULL, 1024, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE); _tcscpy_s(pszData, 1024, szTestData); if (MessageBox(NULL, TEXT("Do you want to access this data later?"), szAppName, MB_YESNO) == IDNO) { // We want this page of storage to remain in our process but the // contents aren't important to us anymore. // Tell the system that the data is not modified. // Note: Because MEM_RESET destroys data, VirtualAlloc rounds // the base address and size parameters to their safest range. // Here is an example: // VirtualAlloc(pvData, 5000, MEM_RESET, PAGE_READWRITE) // resets 0 pages on CPUs where the page size is greater than 4 KB // and resets 1 page on CPUs with a 4 KB page. So that our call to // VirtualAlloc to reset memory below always succeeds, VirtualQuery // is called first to get the exact region size. MEMORY_BASIC_INFORMATION mbi; VirtualQuery(pszData, &mbi, sizeof(mbi)); VirtualAlloc(pszData, mbi.RegionSize, MEM_RESET, PAGE_READWRITE); } // Commit as much storage as there is physical RAM. MEMORYSTATUS mst; GlobalMemoryStatus(&mst); PVOID pvDummy = VirtualAlloc(NULL, mst.dwTotalPhys, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE); // Touch all the pages in the dummy region so that any // modified pages in RAM are written to the paging file. if (pvDummy != NULL) ZeroMemory(pvDummy, mst.dwTotalPhys); // Compare our data page with what we originally wrote there. if (_tcscmp(pszData, szTestData) == 0) { // The data in the page matches what we originally put there. // ZeroMemory forced our page to be written to the paging file. MessageBox(NULL, TEXT("Modified data page was saved."), szAppName, MB_OK); } else { // The data in the page does NOT match what we originally put there // ZeroMemory didn't cause our page to be written to the paging file MessageBox(NULL, TEXT("Modified data page was NOT saved."), szAppName, MB_OK); } // Don't forget to release part of the address space. // Note that it is not mandatory here since the application is exiting. if (pvDummy != NULL) VirtualFree(pvDummy, 0, MEM_RELEASE); VirtualFree(pszData, 0, MEM_RELEASE); return(0);}
