在线等，内存文件映射的问题。

[VCHelp之乐天蛋黄派]

用 CreateFileMapping 成功创建一个文件映射对象，并指定了其大小大于文件实际大小。但是一段时间后发现这个大小的大小需要增加。请问这时候如何操作？

只能关掉文件映射对象重新打开吗？

[赵4老师]

SetFilePointer
The SetFilePointer function moves the file pointer of an open file.

DWORD SetFilePointer(
HANDLE hFile, // handle of file
LONG lDistanceToMove, // number of bytes to move file pointer
PLONG lpDistanceToMoveHigh,
// pointer to high-order DWORD of
// distance to move
DWORD dwMoveMethod // how to move
);

Parameters
hFile
Handle to the file whose file pointer is to be moved. The file handle must have been created with GENERIC_READ or GENERIC_WRITE access to the file.
lDistanceToMove
Low-order 32 bits of a signed value that specifies the number of bytes to move the file pointer. If lpDistanceToMoveHigh is not NULL, lpDistanceToMoveHigh and lDistanceToMove form a single 64-bit signed value that specifies the distance to move. If lpDistanceToMoveHigh is NULL, lDistanceToMove is a 32-bit signed value. A positive value for lDistanceToMove moves the file pointer forward in the file, and a negative value moves the file pointer backward.
lpDistanceToMoveHigh
Pointer to the high-order 32 bits of the signed 64-bit distance to move. If you do not need the high-order 32 bits, this pointer may be NULL. When non-NULL, this parameter also receives the high-order DWORD of the new value of the file pointer. For more information, see the Remarks section later in this topic.
dwMoveMethod
Starting point for the file pointer move. This parameter can be one of the following values. Value Meaning
FILE_BEGIN The starting point is zero or the beginning of the file.
FILE_CURRENT The starting point is the current value of the file pointer.
FILE_END The starting point is the current end-of-file position.


Return Values
If the SetFilePointer function succeeds and lpDistanceToMoveHigh is NULL, the return value is the low-order DWORD of the new file pointer. If lpDistanceToMoveHigh is not NULL, the function returns the low order DWORD of the new file pointer, and puts the high-order DWORD of the new file pointer into the LONG pointed to by that parameter.

If the function fails and lpDistanceToMoveHigh is NULL, the return value is 0xFFFFFFFF. To get extended error information, call GetLastError.

If the function fails, and lpDistanceToMoveHigh is non-NULL, the return value is 0xFFFFFFFF. However, because 0xFFFFFFFF is a valid value for the low-order DWORD of the new file pointer, you must check GetLastError to determine whether an error occurred. If an error occurred, GetLastError returns a value other than NO_ERROR. For a code example that illustrates this point, see the Remarks section later in this topic.

If the new file pointer would have been a negative value, the function fails, the file pointer is not moved, and the code returned by GetLastError is ERROR_NEGATIVE_SEEK.



SetEndOfFile
The SetEndOfFile function moves the end-of-file (EOF) position for the specified file to the current position of the file pointer.

BOOL SetEndOfFile(
HANDLE hFile // handle of file whose EOF is to be set
);

Parameters
hFile
Handle to the file to have its EOF position moved. The file handle must have been created with GENERIC_WRITE access to the file.
Return Values
If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks
This function can be used to truncate or extend a file. If the file is extended, the contents of the file between the old EOF position and the new position are not defined.

If you called CreateFileMapping to create a file-mapping object for hFile, you must first call UnmapViewOfFile to unmap all views and call CloseHandle to close the file-mapping object before you can call SetEndOfFile.

[qq120848369]

munmap => lseek(SEEK_END) => write 1 byte => mmap

[VCHelp之乐天蛋黄派]

引用 2 楼 zhao4zhong1 的回复:

SetFilePointer The SetFilePointer function moves the file pointer of an open file. DWORD SetFilePointer( HANDLE hFile, // handle of file LONG lDistanceToMove, // number of bytes t……

Read my question careful, please.