usr/src/lib/libc/stdio/ftell.c

/*-
 * Copyright (c) 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Chris Torek.
 *
 * %sccs.include.redist.c%
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)ftell.c     8.2 (Berkeley) %G%";
#endif /* LIBC_SCCS and not lint */

#include <stdio.h>
#include <errno.h>
#include "local.h"

/*
 * ftell: return current offset.
 */
long
ftell(fp)
        register FILE *fp;
{
        register fpos_t pos;

        if (fp->_seek == NULL) {
                errno = ESPIPE;                 /* historic practice */
                return (-1L);
        }

        /*
         * Find offset of underlying I/O object, then
         * adjust for buffered bytes.
         */
        if (fp->_flags & __SOFF)
                pos = fp->_offset;
        else {
                pos = (*fp->_seek)(fp->_cookie, (fpos_t)0, SEEK_CUR);
                if (pos == -1L)
                        return (pos);
        }
        if (fp->_flags & __SRD) {
                /*
                 * Reading.  Any unread characters (including
                 * those from ungetc) cause the position to be
                 * smaller than that in the underlying object.
                 */
                pos -= fp->_r;
                if (HASUB(fp))
                        pos -= fp->_ur;
        } else if (fp->_flags & __SWR && fp->_p != NULL) {
                /*
                 * Writing.  Any buffered characters cause the
                 * position to be greater than that in the
                 * underlying object.
                 */
                pos += fp->_p - fp->_bf._base;
        }
        return (pos);
}