BackupRead function (winbase.h)

The BackupRead function can be used to back up a file or directory, including the security information. The function reads data associated with a specified file or directory into a buffer, which can then be written to the backup medium using the WriteFile function.


BOOL BackupRead(
  [in]  HANDLE  hFile,
  [out] LPBYTE  lpBuffer,
  [in]  DWORD   nNumberOfBytesToRead,
  [out] LPDWORD lpNumberOfBytesRead,
  [in]  BOOL    bAbort,
  [in]  BOOL    bProcessSecurity,
  [out] LPVOID  *lpContext


[in] hFile

Handle to the file or directory to be backed up. To obtain the handle, call the CreateFile function. The SACLs are not read unless the file handle was created with the ACCESS_SYSTEM_SECURITY access right. For more information, see File security and access rights.

The handle must be synchronous (nonoverlapped). This means that the FILE_FLAG_OVERLAPPED flag must not be set when CreateFile is called. This function does not validate that the handle it receives is synchronous, so it does not return an error code for a synchronous handle, but calling it with an asynchronous (overlapped) handle can result in subtle errors that are very difficult to debug.

The BackupRead function may fail if CreateFile was called with the flag FILE_FLAG_NO_BUFFERING. In this case, the GetLastError function returns the value ERROR_INVALID_PARAMETER.

[out] lpBuffer

Pointer to a buffer that receives the data.

[in] nNumberOfBytesToRead

Length of the buffer, in bytes. The buffer size must be greater than the size of a WIN32_STREAM_ID structure.

[out] lpNumberOfBytesRead

Pointer to a variable that receives the number of bytes read.

If the function returns a nonzero value, and the variable pointed to by lpNumberOfBytesRead is zero, then all the data associated with the file handle has been read.

[in] bAbort

Indicates whether you have finished using BackupRead on the handle. While you are backing up the file, specify this parameter as FALSE. Once you are done using BackupRead, you must call BackupRead one more time specifying TRUE for this parameter and passing the appropriate lpContext. lpContext must be passed when bAbort is TRUE; all other parameters are ignored.

[in] bProcessSecurity

Indicates whether the function will restore the access-control list (ACL) data for the file or directory.

If bProcessSecurity is TRUE, the ACL data will be backed up.

[out] lpContext

Pointer to a variable that receives a pointer to an internal data structure used by BackupRead to maintain context information during a backup operation.

You must set the variable pointed to by lpContext to NULL before the first call to BackupRead for the specified file or directory. The function allocates memory for the data structure, and then sets the variable to point to that structure. You must not change lpContext or the variable that it points to between calls to BackupRead.

To release the memory used by the data structure, call BackupRead with the bAbort parameter set to TRUE when the backup operation is complete.

Return value

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero, indicating that an I/O error occurred. To get extended error information, call GetLastError.


This function is not intended for use in backing up files encrypted under the Encrypted File System. Use ReadEncryptedFileRaw for that purpose.

If an error occurs while BackupRead is reading data, the calling process can skip the bad data by calling the BackupSeek function.

The file or directory should be restored using the BackupWrite function.


Requirement Value
Minimum supported client Windows XP [desktop apps only]
Minimum supported server Windows Server 2003 [desktop apps only]
Target Platform Windows
Header winbase.h (include Windows.h)
Library Kernel32.lib
DLL Kernel32.dll

See also



Creating a Backup Application