對一個文件使用內存映射文件

Demo:

1:創建或打開一個文件內核對象:

// Open the file for reading and writing.
HANDLE hFile = CreateFile(pszPathname, GENERIC_WRITE | GENERIC_READ, 0,
   NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

// 由于hFile即使為INVALID_HANDLE_VALUE,下面的CreateFileMapping仍然可以正常運行,
// 所以這里一定要對hFile進行檢查!
if (hFile == INVALID_HANDLE_VALUE) {
   chMB("File could not be opened.");
   return(FALSE);
}

2:創建一個文件映射內核對象:

// Get the size of the file (I assume the whole file can be mapped).
DWORD dwFileSize = GetFileSize(hFile, NULL);

// Create the file-mapping object. The file-mapping object is 1 character
// bigger than the file size so that a zero character can be placed at the
// end of the file to terminate the string (file). Because I don't yet know
// if the file contains ANSI or Unicode characters, I assume worst case
// and add the size of a WCHAR instead of CHAR.
HANDLE hFileMap = CreateFileMapping(hFile, NULL, PAGE_READWRITE,
   0,
   dwFileSize + sizeof(WCHAR), // 如果該文件小于設定的大小,本函數將擴展該文件的大小,
          // 使磁盤上的文件變大。這樣當以后將該文件作為內存映射
          // 文件使用時,物理存儲器就已經存在了。
   NULL f// 這個文件映射對象的名字用于與其他進程共享該對象,這里我們還用不到。
   );

if (hFileMap == NULL) {
   chMB("File map could not be opened.");
   CloseHandle(hFile);
   return(FALSE);
}

3:將文件數據映射到進程的地址空間:
當創建了一個文件映射對象之后,仍然必須讓系統為文件的數據保留一個地址空間區域,
并將文件的數據作為映射到該區域的物理存儲器進行提交。

// Get the address where the first byte of the file is mapped into memory.
// the return value is the starting address of the mapped view:
PVOID pvFile = MapViewOfFile(hFileMap, FILE_MAP_WRITE, 0, 0, 0);

if (pvFile == NULL) {
   chMB("Could not map view of file.");
   CloseHandle(hFileMap);
   CloseHandle(hFile);
   return(FALSE);
}

4:既然我們通過pvFile得到了映象視圖的起始地址,那么可以對視圖做一些操作了:
  
ANSI版本:
PSTR pchANSI = (PSTR) pvFile;
UNICODE版本:
PWSTR pchUnicode = (PWSTR) pvFile;

5:從進程的地址空間中撤銷文件數據的映象:

// Clean up everything before exiting.
UnmapViewOfFile(pvFile);

6:關閉文件映射對象和文件對象:

CloseHandle(hFileMap);
CloseHandle(hFile);

Definition:

HANDLE CreateFileMapping(
  HANDLE hFile,                       // handle to file
  LPSECURITY_ATTRIBUTES lpAttributes, // security
  DWORD flProtect,                    // protection
  DWORD dwMaximumSizeHigh,            // high-order DWORD of size
  DWORD dwMaximumSizeLow,             // low-order DWORD of size
  LPCTSTR lpName                      // object name
);
LPVOID MapViewOfFile(
  HANDLE hFileMappingObject,   // handle to file-mapping object
  DWORD dwDesiredAclearcase/" target="_blank" >ccess,       // access mode
  DWORD dwFileOffsetHigh,      // high-order DWORD of offset
  DWORD dwFileOffsetLow,       // low-order DWORD of offset
  SIZE_T dwNumberOfBytesToMap  // number of bytes to map
);
BOOL UnmapViewOfFile(
  LPCVOID lpBaseAddress   // starting address
);

Tips:
也可以盡量早地把對象關閉,以消除資源泄漏的可能性,如:
HANDLE hFile = CreateFile(...);
HANDLE hFileMapping = CreateFileMapping(hFile,...);
CloseHandle(hFile);

PVOID pvFile = MapViewOfFile(hFileMapping,...);
CloseHandle(hFileMapping);

// use the memory-mapped file.

UnmapViewOfFile(pvFile);

原文轉自：http://www.anti-gravitydesign.com