V4/man/man3/getc.3

.th GETC III 4/30/72
.sh NAME
getc  \*-  buffered input
.sh SYNOPSIS
.ft B
mov	$filename,r0
.br
jsr	r5,fopen; iobuf
.s3
fopen(filename, iobuf)
.br
char *filename;
.br
struct buf *iobuf;
.s3
jsr	r5,getc; iobuf
.br
.ft R
(character in r0)
.s3
.ft B
getc(iobuf)
.br
struct buf *iobuf;
.s3
jsr	r5,getw; iobuf
.br
.ft R
(word in r0)
.s3
[getw not available in C]
.sh DESCRIPTION
These routines provide a buffered input
facility.
.it Iobuf
is the address of a 518(10) byte buffer area whose
contents are maintained by these routines.  Its format is:
.s3
.nf
.ft B
ioptr:	.=.+2		/ file descriptor
	.=.+2		/ characters left in buffer
	.=.+2		/ ptr to next character
	.=.+512.	/ the buffer
.ft R
.s3
Or in C,
.s3
.ft B
	struct buf {
		int fildes;
		int nleft;
		char *nextp;
		char buffer[512];
	};
.ft R
.s3
.fi
.it Fopen
may be called initially to open the file.  On return,
the error bit (c-bit) is set if the open failed.
If \fIfopen\fR is never called, \fIget\fR will
read from the standard
input file.
From C, the value is negative if the open failed.
.s3
.it Getc
returns the next byte from the file in r0.  The
error bit is set on end of file or a read error.
From C, the character is returned;
it is \*-1 on end-of-file or error.
.s3
\fIGetw\fR returns the next word in r0.
.it Getc
and
\fIgetw\fR
may be used alternately; there are no odd/even
problems.
\fIGetw\fR is not available from C.
.s3
.it Iobuf
must be provided by the user; it must be on a word boundary.
.s3
To reuse the same buffer for another file, it is sufficient
to close the original file and call \fIfopen\fR again.
.sh "SEE ALSO"
open(II), read(II), putc(III)
.sh DIAGNOSTICS
c-bit set on EOF or error;
.br
from C, negative return indicates error or EOF.
.sh BUGS