getc.3

UNIX版本6的源代码

.th GETC III 4/30/72
.sh NAME
getc, getw, fopen  \*-  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
.ft B
getw(iobuf)
.br
struct buf *iobuf;
.ft R
.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 structure is
.s3
.nf
.ft B
	struct buf {
		int fildes;	/* File descriptor */
		int nleft;	/* Chars left in buffer */
		char *nextp;	/* Ptr to next character */
		char buff[512];	/* The buffer */
	};
.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 as an integer, without sign extension;
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 may be called from C;
\*-1 is returned on end-of-file or error,
but of course
is also a legitimate value.
.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), getchar (III), putc (III)
.sh DIAGNOSTICS
c-bit set on EOF or error;
from C, negative return indicates error or EOF.
Moreover,
.it errno
is set by this routine just as it is for a system call
(see introduction (II)).
.sh BUGS