.hd writef "write raw words to file" 03/25/82
integer function writef (buf, nw, fd)
integer buf (ARB), nw
file_des fd
.sp
Library:  vswtlb (standard Subsystem library)
.fs
'Writef' is used to write words to a file, which may be assigned to any
device recognized by the Subsystem.
(A word on the Prime is 16 bits long.)
The first argument is a string of words to be written to the
file; the second argument is the number of words to be written;
the third argument is the file descriptor of the file to which data
will be written.  Words are transferred from the string buffer to the
file until  'nw'  words are written.
The function return is ERR if the file is not writeable, if the given
file descriptor is invalid, or if the file's error flag is set;
otherwise, the function return is the number of words written
(nominally the same as 'nw').
Exceptions:  a write on the null device (/dev/null) always returns
EOF, and an error detected by Primos causes a return of EOF.
.im
'Writef' calls 'mapsu' to convert standard port numbers into file
descriptors.
If the last operation performed on the file was not a 'writef',
'flush$' is called to empty the file's buffers.
Depending on the device type associated with the file, one of the device
dependent drivers 'dwrit$' (for disk files) or 'twrit$' (for terminal files)
is called to perform the actual data transfer.
.ca
mapsu, dwrit$, twrit$, flush$
.bu
Support for more devices would be nice.
.sp
EOF is
returned if any error occurs when writing to disk (in dwrit$); the user
is not informed of the actual error that occurs.
.sa
mapsu (2), dwrit$ (6), twrit$ (6), flush$ (6)