FlushFileBuffers function
Applies to: desktop apps | Metro style apps
Flushes the buffers of a specified file and causes all buffered data to be written to a file.
Syntax
BOOL WINAPI FlushFileBuffers( __in HANDLE hFile );
Parameters
- hFile [in]
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A handle to the open file.
The file handle must have the GENERIC_WRITE access right. For more information, see File Security and Access Rights.
If hFile is a handle to a communications device, the function only flushes the transmit buffer.
If hFile is a handle to the server end of a named pipe, the function does not return until the client has read all buffered data from the pipe.
Return value
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.
The function fails if hFile is a handle to the console output. That is because the console output is not buffered. The function returns FALSE, and GetLastError returns ERROR_INVALID_HANDLE.
Remarks
Typically the WriteFile and WriteFileEx functions write data to an internal buffer that the operating system writes to a disk or communication pipe on a regular basis. The FlushFileBuffers function writes all the buffered information for a specified file to the device or pipe.
Due to disk caching interactions within the system, the FlushFileBuffers function can be inefficient when used after every write to a disk drive device when many writes are being performed separately. If an application is performing multiple writes to disk and also needs to ensure critical data is written to persistent media, the application should use unbuffered I/O instead of frequently calling FlushFileBuffers. To open a file for unbuffered I/O, call the CreateFile function with the FILE_FLAG_NO_BUFFERING and FILE_FLAG_WRITE_THROUGH flags. This prevents the file contents from being cached and flushes the metadata to disk with each write. For more information, see CreateFile.
To flush all open files on a volume, call FlushFileBuffers with a handle to the volume. The caller must have administrative privileges. For more information, see Running with Special Privileges.
When opening a volume with CreateFile, the lpFileName string should be the following form: \\.\x: or \\?\Volume{GUID}. Do not use a trailing backslash in the volume name, because that indicates the root directory of a drive.
Examples
For an example, see Multithreaded Pipe Server.
Requirements
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Minimum supported client | Windows XP |
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Minimum supported server | Windows Server 2003 |
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See also
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Build date: 4/17/2012
A large series of fwrite() calls is interrupted by jumping backwards some kbytes using fseek(), re-writing a few bytes using fwrite(), returning to previous position using fseek(), then continue with multiple fwrite() calls.
The single writing call at the outlying backward position is dropped. The previous contents of this region is retained. Maybe the write is treated like an asynchronous write since it affects a different file sector. All function calls return success.
The problem does not occur when running on Win XP.
- 2/7/2011
- Larix A
- 8/24/2010
- Kirby Trump
