内存映射文件实例

『壹』 鍐呭瓨鏄犲皠鏂囦欢鐨勫簲鐢ㄧず渚

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// 鍒涘缓鏂囦欢鍐呮牳瀵硅薄锛屽叾鍙ユ焺淇濆瓨浜巋File
HANDLE hFile = CreateFile(Recv1.zip,GENERIC_WRITE | GENERIC_READ,FILE_SHARE_READ,NULL,CREATE_ALWAYS,FILE_FLAG_SEQUENTIAL_SCAN,NULL);
// 鍒涘缓鏂囦欢鏄犲皠鍐呮牳瀵硅薄锛屽彞鏌勪繚瀛樹簬hFileMapping
HANDLE hFileMapping = CreateFileMapping(hFile,NULL,PAGE_READWRITE,0,0x4000000,NULL);
// 閲婃斁鏂囦欢鍐呮牳瀵硅薄
CloseHandle(hFile);
// 璁惧畾澶у皬銆佸亸绉婚噺绛夊弬鏁 // 灏介噺鎶婃枃浠惰剧疆澶т竴浜涳紝 濡傛灉鍐欑殑鏁版嵁瓒呰繃锛岃惧畾鐨勫硷紝鍐嶆℃槧灏勬枃浠朵細鎶ラ敊 getlasterror = 183;
__int64 qwFileSize = 0x4000000;
__int64 qwFileOffset = 0;
__int64 T = 600 * sinf.dwAllocationGranularity;
DWORD dwBytesInBlock = 1000 * sinf.dwAllocationGranularity;
// 灏嗘枃浠舵暟鎹鏄犲皠鍒拌繘绋嬬殑鍦板潃绌洪棿
PBYTE pbFile = (PBYTE)MapViewOfFile(hFileMapping,FILE_MAP_ALL_ACCESS,(DWORD)(qwFileOffset>>32),(DWORD)(qwFileOffset&0xFFFFFFFF),dwBytesInBlock);
while(bLoop)
{
// 鎹曡幏浜嬩欢hEvent[0]鍜屼簨浠秇Event[1]
DWORD ret = WaitForMultipleObjects(2,hEvent,FALSE,INFINITE);
ret -= WAIT_OBJECT_0;
switch (ret)
{
// 鎺ユ敹鏁版嵁浜嬩欢瑙﹀彂
case 0:
// 浠庣鍙ｆ帴鏀舵暟鎹骞朵繚瀛樺埌鍐呭瓨鏄犲皠鏂囦欢
nReadLen=syio_Read(port[1],pbFile + qwFileOffset,QueueLen);
qwFileOffset += nReadLen;
// 褰撴暟鎹鍐欐弧60%鏃讹紝涓洪槻鏁版嵁婧㈠嚭锛岄渶瑕佸湪鍏跺悗寮杈熶竴鏂扮殑鏄犲皠瑙嗗浘
if (qwFileOffset > T)
{
T = qwFileOffset + 600 * sinf.dwAllocationGranularity;UnmapViewOfFile(pbFile);
pbFile = (PBYTE)MapViewOfFile(hFileMapping,FILE_MAP_ALL_ACCESS,(DWORD)(qwFileOffset>>32),(DWORD)(qwFileOffset&0xFFFFFFFF),dwBytesInBlock);
}
break;
// 缁堟浜嬩欢瑙﹀彂
case 1:
bLoop = FALSE;
// 浠庤繘绋嬬殑鍦板潃绌洪棿鎾ゆ秷鏂囦欢鏁版嵁鏄犲儚
UnmapViewOfFile(pbFile);
// 鍏抽棴鏂囦欢鏄犲皠瀵硅薄
CloseHandle(hFileMapping);
break;
}
}鈥
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// 鍒涘缓鍙﹀栦竴涓鏂囦欢鍐呮牳瀵硅薄
hFile2 = CreateFile(Recv.zip,GENERIC_WRITE | GENERIC_READ,FILE_SHARE_READ,NULL,CREATE_ALWAYS,FILE_FLAG_SEQUENTIAL_SCAN,NULL);
// 浠ュ疄闄呮暟鎹闀垮害鍒涘缓鍙﹀栦竴涓鏂囦欢鏄犲皠鍐呮牳瀵硅薄
hFileMapping2 = CreateFileMapping(hFile2,NULL,PAGE_READWRITE,0,(DWORD)(qwFileOffset&0xFFFFFFFF),NULL);
// 鍏抽棴鏂囦欢鍐呮牳瀵硅薄
CloseHandle(hFile2);
// 灏嗘枃浠舵暟鎹鏄犲皠鍒拌繘绋嬬殑鍦板潃绌洪棿
pbFile2 = (PBYTE)MapViewOfFile(hFileMapping2,FILE_MAP_ALL_ACCESS,0,0,qwFileOffset);
// 灏嗘暟鎹浠庡師鏉ョ殑鍐呭瓨鏄犲皠鏂囦欢澶嶅埗鍒版ゅ唴瀛樻槧灏勬枃浠
memcpy(pbFile2,pbFile,qwFileOffset);
file:
//浠庤繘绋嬬殑鍦板潃绌洪棿鎾ゆ秷鏂囦欢鏁版嵁鏄犲儚
UnmapViewOfFile(pbFile);
UnmapViewOfFile(pbFile2);
// 鍏抽棴鏂囦欢鏄犲皠瀵硅薄
CloseHandle(hFileMapping);
CloseHandle(hFileMapping2);
// 鍒犻櫎涓存椂鏂囦欢
DeleteFile(Recv1.zip);

『贰』 内存映射文件 存储空间不够、

设一个偏移量，不要映射那么多。下面是别人的处理方法，抄来给你：

使用内存映射文件处理大文件的代码示例：

1 SYSTEM_INFO sinf;
2 GetSystemInfo(&sinf);
3
4 // Open the file for reading and writing.
5 HANDLE hFile = CreateFile(pszPathname, GENERIC_WRITE | GENERIC_READ, 0,
6 NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
7 if (hFile == INVALID_HANDLE_VALUE) {
8 chMB("File could not be opened.");
9 return(FALSE);
10 }
11
12 // Get the size of the file (I assume the whole file can be mapped) in bytes.
13 DWORD dwFileSize = GetFileSize(hFile, NULL);
14
15 // Create the file-mapping object.
16 HANDLE hFileMap = CreateFileMapping(hFile, NULL, PAGE_READWRITE,
17 0, dwFileSize, NULL);
18 if (hFileMap == NULL) {
19 chMB("File map could not be opened.");
20 CloseHandle(hFile);
21 return(FALSE);
22 }
23
24 DWORD map_data_offset = 0;
25 DWORD bytes_mapped = sinf.dwAllocationGranularity;
26 PVOID pvFile = NULL;
27 PSTR ps_ptr = NULL;
28
29 while(dwFileSize > 0)
30 {
31 if(dwFileSize < bytes_mapped)
32 {
33 pvFile = MapViewOfFile(hFileMap, FILE_MAP_WRITE, 0, map_data_offset, dwFileSize);
34 //对字符数组pvFile的处理
35 map_data_offset += dwFileSize;
36 dwFileSize = 0;
37 }
38 else
39 {
40 pvFile = MapViewOfFile(hFileMap,FILE_MAP_WRITE,0,map_data_offset,bytes_mapped);
41 //对字符数组pvFile的处理
42 map_data_offset += bytes_mapped;
43 dwFileSize -= bytes_mapped;
44 }
45 }
46 // Clean up everything before exiting.
47 UnmapViewOfFile(pvFile);
48 CloseHandle(hFileMap);
49 // Remove trailing zero character added earlier.
50 SetFilePointer(hFile, dwFileSize, NULL, FILE_BEGIN);
51 CloseHandle(hFile);
文件映射对象存储于内核地址范围是所有操作系统的进程共享的，而MapViewOfFile文件映射地址空间是存在于进程的私有地址空间中，要想指定地址空间首地址可用MapViewOfFileEx函数，但只是建议首地址。

『叁』 怎样用C++内存映射磁盘文件的方式映射一个几百M的文件，还有几十M，还有几十K的文件

#include <windows.h>
#include <tchar.h>
#include <stdio.h>
int main()
{
HANDLE hFile = CreateFile(_T("1.txt"), GENERIC_READ | GENERIC_WRITE, 0, 0, CREATE_ALWAYS, 0, 0);
if (hFile == INVALID_HANDLE_VALUE) {
puts("fail to create file");
goto fail_open;
}

SetFileValidData(hFile, 1024);

HANDLE hMap = CreateFileMapping(hFile, 0, PAGE_READWRITE, 0, 1024, 0);
if (hMap == NULL) {
puts("fail to create mapping");
goto fail_map;
}

LPVOID pContent = MapViewOfFile(hMap, FILE_MAP_WRITE, 0, 0, 1024);
if (pContent == 0) {
puts("fail to open mapping");
goto fail_view;
}

//好了，此时这个文件就相当于你用malloc申请的一个1024字节的内存空间。
char* pStr = (char*) pContent;
strcpy(pStr, "hahaha");

UnmapViewOfFile(pContent);
fail_view:
CloseHandle(hMap);
fail_map:
CloseHandle(hFile);
fail_open:
return 0;
}

『肆』 我c++要处理大量数据,一个都是几百m,如何存入内存.

用内存映射应该行的。内存映射就是把一个文件当作一块内存区域用。

类别: 内存映射文件

题目:对一个文件使用内存映射文件

Demo:

1:创建或打开一个文件内核对象:

// 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即使为INVALID_HANDLE_VALUE,下面的CreateFileMapping仍然可以正常运行,
// 所以这里一定要对hFile进行检查!
if (hFile == INVALID_HANDLE_VALUE) {
chMB("File could not be opened.");
return(FALSE);
}

2:创建一个文件映射内核对象:

// 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), // 如果该文件小于设定的大小,本函数将扩展该文件的大小,
// 使磁盘上的文件变大。这样当以后将该文件作为内存映射
// 文件使用时,物理存储器就已经存在了。
NULL f// 这个文件映射对象的名字用于与其他进程共享该对象,这里我们还用不到。
);

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

3:将文件数据映射到进程的地址空间:
当创建了一个文件映射对象之后,仍然必须让系统为文件的数据保留一个地址空间区域,
并将文件的数据作为映射到该区域的物理存储器进行提交。

// 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:既然我们通过pvFile得到了映象视图的起始地址,那么可以对视图做一些操作了:

ANSI版本:
PSTR pchANSI = (PSTR) pvFile;
UNICODE版本:
PWSTR pchUnicode = (PWSTR) pvFile;

5:从进程的地址空间中撤销文件数据的映象:

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

6:关闭文件映射对象和文件对象:

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 dwDesiredAccess, // 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:
也可以尽量早地把对象关闭,以消除资源泄漏的可能性,如:
HANDLE hFile = CreateFile(...);
HANDLE hFileMapping = CreateFileMapping(hFile,...);
CloseHandle(hFile);

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

// use the memory-mapped file.

UnmapViewOfFile(pvFile);