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#define INCL_DOSFILEMGR
 
USHORT DosWriteAsync(hf, hsemRam, pusErrCode, pvBuf, cbBuf,
    pcbBytesWritten)
HFILE hf;                   /* file handle                                */
PULONG hsemRam;             /* pointer to RAM semaphore                   */
PUSHORT pusErrCode;         /* pointer to variable for error value        */
PVOID pvBuf;                /* pointer to buffer containing data to write */
USHORT cbBuf;               /* number of bytes in buffer                  */
PUSHORT pcbBytesWritten;    /* pointer to variable for bytes written      */
 
The DosWriteAsync function writes one or more bytes of data to a specified
file. The function writes the data asynchronously──that is, the function
returns immediately, but continues to copy data to the specified file while
the process continues with other tasks.
 
Parameter        Description
────────────────────────────────────────────────────────────────────────────
 
hf               Identifies the file that receives the data. This handle
                 must have been created previously by using the DosOpen
                 function.
 
hsemRam          Points to the RAM semaphore that indicates when the
                 function has finished reading the data.
 
pusErrCode       Points to the variable that receives an error value.
 
pvBuf            Points to the buffer that contains the data to write.
 
cbBuf            Specifies the number of bytes to write.
 
pcbBytesWritten  Points to the variable receiving the number of bytes
                 written.
 
Return Value
 
The return value is zero if the function is successful. Otherwise, it is an
error value, which may be one of the following:
 
     ERROR_ACCESS_DENIED
     ERROR_BROKEN_PIPE
     ERROR_INVALID_HANDLE
     ERROR_LOCK_VIOLATION
     ERROR_NO_PROC_SLOTS
     ERROR_NOT_DOS_DISK
     ERROR_WRITE_FAULT
 
Comments
 
The DosWriteAsync function starts writing at the current file-pointer
position. The file-pointer position can be changed by using the
DosChgFilePtr function.
 
If the specified file has been opened using the write-through flag, the
DosWriteAsync function writes data to an internal file buffer and to the
disk before returning. If the write-through flag has not been set, the
system collects the data in an internal file buffer and writes the data to
the disk only when the buffer is full.
 
The DosWriteAsync function may write fewer bytes to the file than the number
specified in the cbBuf parameter if there is not enough space on the disk
for all the requested bytes. The cbBuf parameter can be zero without causing
an error──that is, writing no bytes is acceptable.
 
When the DosWriteAsync function has written the data, it clears the RAM
semaphore pointed to by the hsemRam parameter. If the process uses the
semaphore to determine when data is available, it must use the DosSemSet
function to set the semaphore before calling DosWriteAsync.
 
The efficiency with which the DosWriteAsync function writes to a disk is
improved when the cbBuf parameter is set to a multiple of the disk's
bytes-per-sector size. When cbBuf is set this way, the function writes
directly to the disk, without first copying the data to an internal file
buffer. (The DosQFSInfo function retrieves the bytes-per-sector value for a
disk.)
 
DosWriteAsync can be used to write bytes or messages to a pipe. Each write
to a message pipe writes a message whose size is specified by the cbBuf
parameter; DosWriteAsync automatically encodes message lengths in the pipe,
so applications need not encode this information in the buffer being
written.
 
In blocking mode, write operations always write all requested bytes before
returning. In nonblocking mode, write operations return either with all
bytes written or none written; the latter occurs in cases where
DosWriteAsync has to block in order to complete the request (for example, if
there is no room in the pipe buffer or if the buffer is currently being
written to by another process).
 
When the function tries to write to a pipe whose other end has been closed,
it returns the error ERROR_BROKEN_PIPE.
 
Example
 
This example creates the file abc.ext, sets a RAM semaphore, and calls the
DosWriteAsync function to write the contents of the buffer abBuf to a file.
When any additional processing is finished, the example calls the
DosSemWait function to wait until DosWriteAsync has finished writing to the
file.
 
ULONG hsemWrite = 0;
BYTE abBuf[1024];
HFILE hf;
USHORT usAction, cbBytesWritten;
USHORT usWriteAsyncError;
DosOpen("abc.ext", &hf, &usAction, 0L, FILE_NORMAL,
    FILE_CREATE,
    OPEN_ACCESS_WRITEONLY | OPEN_SHARE_DENYWRITE, 0L);
 
DosSemSet(&hsemWrite);         /* sets semaphore           */
DosWriteAsync(hf,              /* file handle              */
    &hsemWrite,                /* semaphore address        */
    &usWriteAsyncError,        /* return-code address      */
    abBuf,                     /* buffer address           */
    sizeof(abBuf),             /* buffer size              */
    &cbBytesWritten);          /* address of bytes written */
    .
    . /* Other processing would go here. */
    .
DosSemWait(&hsemWrite, -1L);   /* waits for DosWriteAsync  */
if (usWriteAsyncError) {
    .
    . /* Error processing would go here. */
    .
 
See Also
 
DosChgFilePtr, DosOpen, DosQFSInfo, DosReadAsync, DosSemSet, DosSemWait,
DosWrite
 
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