ReadFile
A version of this page is also available for
4/8/2010
This function reads data from a file, starting at the position indicated by the file pointer. After the read operation has been completed, the file pointer is adjusted by the number of bytes read.
Syntax
BOOL ReadFile(
HANDLE hFile,
LPVOID lpBuffer,
DWORD nNumberOfBytesToRead,
LPDWORD lpNumberOfBytesRead,
LPOVERLAPPED lpOverlapped
);
Parameters
- hFile
[in] Handle to the file to be read. The file handle must have been created with GENERIC_READ access to the file. This parameter cannot be a socket handle.
- lpBuffer
[out] Pointer to the buffer that receives the data read from the file.
- nNumberOfBytesToRead
[in] Number of bytes to be read from the file.
- lpNumberOfBytesRead
[out] Pointer to the number of bytes read. This function sets this value to zero before taking action or checking errors.
- lpOverlapped
[in] Unsupported. Set to NULL.
Return Value
Nonzero indicates success. Zero indicates failure. To get extended error information, call GetLastError.
If the return value is nonzero and the number of bytes read is zero, the file pointer was beyond the current end of the file at the time of the read operation.
Remarks
If part of the file is locked by another process and the read operation overlaps the locked portion, this function fails.
Accessing the input buffer while a read operation is using the buffer can cause corruption of the data read into that buffer. Applications must not read from, write to, reallocate, or free the input buffer that a read operation is using until the read operation completes.
When reading from a communications device, the behavior of this function is governed by the current communication time-outs as set and retrieved using the SetCommTimeouts and the GetCommTimeouts functions. Unpredictable results can occur if you fail to set the time-out values. For more information on communication time-outs, see COMMTIMEOUTS.
This function can fail and return ERROR_INVALID_USER_BUFFER or ERROR_NOT_ENOUGH_MEMORY when there are too many outstanding asynchronous I/O requests.
When a read operation reaches the end of a file, this function returns TRUE and sets *lpNumberOfBytesRead to zero. Windows Embedded CE does not support asynchronous read operations on files. The following code sample shows a test for the end of the file:
// Attempt a synchronous read operation.
bResult = ReadFile(hFile, &inBuffer, nBytesToRead, &nBytesRead, NULL) ;
// Check for end of file.
if (bResult && (nBytesRead == 0) )
{
// you are at the end of the file.
}
Requirements
| Header | winbase.h |
| Library | coredll.lib |
| Windows Embedded CE | Windows CE 1.0 and later |
| Windows Mobile | Windows Mobile Version 5.0 and later |