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Inside Macintosh: Devices /

Chapter 1 - Device Manager / Device Manager Reference

Device Manager Functions / Communicating With Device Drivers

FSWrite

You can use the FSWrite function to write data from a data buffer to an open driver.

pascal OSErr FSWrite(short refNum, long *count, 
                     const void *buffPtr); 

refNum

The driver reference number.

count

The number of bytes to write.

buffPtr

A pointer to the buffer that holds the data.

DESCRIPTION

The FSWrite function attempts to write the number of bytes indicated by the count parameter from the data buffer pointed to by the buffPtr parameter to the device driver specified by the refNum parameter. After the transfer is complete, the count parameter indicates the number of bytes actually written.

The FSWrite function is a high-level synchronous version of the low-level PBWrite function. Use the PBWrite function when you want to request asynchronous writing or need to specify a drive number or a positioning mode and offset. See the next section, which describes the PBWrite function.

SPECIAL CONSIDERATIONS

Do not call the FSWrite function at interrupt time. Synchronous requests at interrupt time may block other pending I/O requests and cause the Device Manager to loop indefinitely while it waits for the device driver to complete the interrupted requests.

RESULT CODES

noErr	0	No error
writErr	-20	Driver does not respond to write requests
badUnitErr	-21	Driver reference number does not match unit table
unitEmptyErr	-22	Driver reference number specifies a nil handle in unit table
abortErr	-27	Request aborted by KillIO
notOpenErr	-28	Driver not open

SEE ALSO

For information about the low-level function for writing to device drivers, see the next section, which describes the PBWrite function.