大于4G的文件用什么读写?
文件映射不好定位,不用了,还有什么办法?

[解决办法]
使用
DWORD CFile:: ReadHuge( void* lpBuffer, DWORD dwCount );
void CFile::WriteHuge( const void* lpBuf, DWORD dwCount );

[解决办法]
内存影射文件，或则自己写类似的代码。用到才读写
[解决办法]
使用重叠结构指定文件位置：


OVERLAPPED ov = { 0, 0, 0, 0, NIULL };
RECORD r;
LONGLONG n;
LARGE_INTEGER FilePos;
DWORD nRead, nWrite;

FilePos.QuadPart = n * sizeof(RECORD);
ov.offset = FilePos.LowPart;
ov.offsetHigh = FilePos.HighPart;
ReadFile(hFile, r, sizeof(RECORD), &nRead, &ov);
WriteFile(hFile, r, sizeof(RECORD), &nWrite,&ov);
[解决办法]
下面的来自Windows核心编程第17章，你可以从那里得到更多的信息。

Processing a Big File Using Memory-Mapped Files
In an earlier section, I said I would tell you how to map a 16-EB file into a small address space. Well, you can 't. Instead, you must map a view of the file that contains only a small portion of the file 's data. You should start by mapping a view of the very beginning of the file. When you 've finished accessing the first view of the file, you can unmap it and then map a new view starting at an offset deeper within the file. You 'll need to repeat this process until you access the complete file. This certainly makes dealing with large memory-mapped files less convenient, but fortunately most files are small enough that this problem doesn 't usually come up.

Let 's look at an example using an 8-GB file and a 32-bit address space. Here is a routine that counts all the 0 bytes in a binary data file in several steps:

__int64 Count0s(void)
{
//View must always start on a multiple
//of the allocation granularity
SYSTEM_INFO sinf;
GetSystemInfo(&sinf);

//Open the data file.
HANDLE hFile = CreateFile( "C:\\HugeFile.Big ", GENERIC_READ,
FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_FLAG_SEQUENTIAL_SCAN, NULL);
//Create the file-mapping object
HANDLE hFileMapping = CreateFileMapping(hFile, NULL,
PAGE_READONLY, 0, 0, NULL);

DWORD dwFileSizeHigh;
__int64 qwFileSize = GetFileSize(hFile, &dwFileSizeHigh);
qwFileSize += (((__int64)dwFileSizeHigh) < <32);

//We no longer need access to the file object 's handle.
CloseHandle(hFile);

__int64 qwFileOffset = 0;
__int64 qwNumOf0s = 0;

while (qwFileSize > 0)
{
//Determine the number of bytes to be mapped in this view
DWORD dwBytesInBlock = sinf.dwAllocationGranularity;
if (qwFileSize < sinf.dwAllocationGranularity)
dwBytesInBlock = (DWORD)qwFileSize;

PBYTE pbFile = (PBYTE)MapViewOfFile(hFileMapping, FILE_MAP_READ,
(DWORD)(qwFileOffset> > 32),
(DWORD)(qwFileOffset & 0xFFFFFFFF),
dwBytesInBlock);

//Count the number of Js in this block.
for (DWORD dwByte = 0; dwByte < dwBytesInBlock; dwByte++)
{
if (pbFile[dwByte] == 0)
qwNumOf0s++;
}

//Unmap the view; we don 't want multiple views
//in our address space
UnmapViewOfFile(pbFile);

//Skip to the next set of bytes in the file.
qwFileOffset += dwBytesInBlock;
qwFileSize -= dwBytesInBlock;

}

CloseHandle(hFileMapping);
return qwNumOf0s;
}



This algorithm maps views of 64 KB (the allocation granularity size) or less. Also, remember that MapViewOfFile requires that the file offset parameters be a multiple of the allocation granularity size. As each view is mapped into the address space, the scanning for zeros continues. After each 64-KB chunk of the file has been mapped and scanned, it 's time to tidy up by closing the file-mapping object.