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/*

 * Copyright (c) 1990 The Regents of the University of California.

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms are permitted

 * provided that the above copyright notice and this paragraph are

 * duplicated in all such forms and that any documentation,

 * advertising materials, and other materials related to such

 * distribution and use acknowledge that the software was developed

 * by the University of California, Berkeley.  The name of the

 * University may not be used to endorse or promote products derived

 * from this software without specific prior written permission.

 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED

 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

 */

/*

FUNCTION

<<ftell>>---return position in a stream or file

INDEX

        ftell

ANSI_SYNOPSIS

        #include <stdio.h>

        long ftell(FILE *<[fp]>);

TRAD_SYNOPSIS

        #include <stdio.h>

        long ftell(<[fp]>)

        FILE *<[fp]>;

DESCRIPTION

Objects of type <<FILE>> can have a ``position'' that records how much

of the file your program has already read.  Many of the <<stdio>> functions

depend on this position, and many change it as a side effect.

The result of <<ftell>> is the current position for a file

identified by <[fp]>.  If you record this result, you can later

use it with <<fseek>> to return the file to this

position.

In the current implementation, <<ftell>> simply uses a character

count to represent the file position; this is the same number that

would be recorded by <<fgetpos>>.

RETURNS

<<ftell>> returns the file position, if possible.  If it cannot do

this, it returns <<-1L>>.  Failure occurs on streams that do not support

positioning; the global <<errno>> indicates this condition with the

value <<ESPIPE>>.

PORTABILITY

<<ftell>> is required by the ANSI C standard, but the meaning of its

result (when successful) is not specified beyond requiring that it be

acceptable as an argument to <<fseek>>.  In particular, other

conforming C implementations may return a different result from

<<ftell>> than what <<fgetpos>> records.

No supporting OS subroutines are required.

*/

#if defined(LIBC_SCCS) && !defined(lint)

static char sccsid[] = "%W% (Berkeley) %G%";

#endif /* LIBC_SCCS and not lint */

/*

 * ftell: return current offset.

 */

#include <stdio.h>

#include <errno.h>

#include "local.h"

long

_DEFUN (ftell, (fp),

        register FILE * fp)

{

  fpos_t pos;

  /* Ensure stdio is set up.  */

  CHECK_INIT (fp);

  if (fp->_seek == NULL)

    {

      fp->_data->_errno = ESPIPE;

      return -1L;

    }

  /* Find offset of underlying I/O object, then

     adjust for buffered bytes.  */

  fflush(fp);           /* may adjust seek offset on append stream */

  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;

}