1 /* FTELL.C

     2  * 

     3  * Portions Copyright (c) 1990-1999 Nokia Corporation and/or its subsidiary(-ies).

     4  * All rights reserved.

     5  */

     6 

     7 /*

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

     9  * All rights reserved.

    10  *

    11  * Redistribution and use in source and binary forms are permitted

    12  * provided that the above copyright notice and this paragraph are

    13  * duplicated in all such forms and that any documentation,

    14  * advertising materials, and other materials related to such

    15  * distribution and use acknowledge that the software was developed

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

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

    18  * from this software without specific prior written permission.

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

    20  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED

    21  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

    22  */

    23 

    24 /*

    25 FUNCTION

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

    27 

    28 INDEX

    29 	ftell

    30 

    31 ANSI_SYNOPSIS

    32 	#include <stdio.h>

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

    34 

    35 TRAD_SYNOPSIS

    36 	#include <stdio.h>

    37 	long ftell(<[fp]>)

    38 	FILE *<[fp]>;

    39 

    40 DESCRIPTION

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

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

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

    44 

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

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

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

    48 position.

    49 

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

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

    52 would be recorded by <<fgetpos>>.

    53 

    54 RETURNS

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

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

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

    58 value <<ESPIPE>>.

    59 

    60 PORTABILITY

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

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

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

    64 conforming C implementations may return a different result from

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

    66 

    67 No supporting OS subroutines are required.

    68 */

    69 

    70 /*

    71  * ftell: return current offset.

    72  */

    73 

    74 #include <stdio_r.h>

    75 #include <errno.h>

    76 

    77 #include "LOCAL.H"

    78 

    79 /**

    80 Return the current position in a stream.

    81 Returns the current position pointed by the position indicator of the stream. 

    82 When a file has been opened in binary mode the value obtained corresponds to 

    83 the number of bytes from the beginning of the file. In files opened in 

    84 text-mode this is not granted because of carriage-return translations under that mode.

    85 @return On success, the current file pointer position is returned.

    86 If an error occurs -1 is returned.

    87 @param Pointer to an open file.

    88 */

    89 EXPORT_C long

    90 ftell (FILE * fp)

    91 {

    92   fpos_t pos;

    93 

    94   /* Ensure stdio is set up.  */

    95 

    96   CHECK_INIT (fp);

    97 

    98   if (fp->_seek == NULL)

    99     {

   100       __errno_r(fp->_data) = ESPIPE;

   101       return -1L;

   102     }

   103 

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

   105      adjust for buffered bytes.  */

   106 

   107   if (fp->_flags & __SOFF)

   108     pos = fp->_offset;

   109   else

   110     {

   111       pos = (*fp->_seek) (fp->_cookie, (fpos_t) 0, SEEK_CUR);

   112       if (pos == -1L)

   113 	return pos;

   114     }

   115   if (fp->_flags & __SRD)

   116     {

   117       /*

   118        * Reading.  Any unread characters (including

   119        * those from ungetc) cause the position to be

   120        * smaller than that in the underlying object.

   121        */

   122       pos -= fp->_r;

   123       if (HASUB (fp))

   124 	pos -= fp->_ur;

   125     }

   126   else if (fp->_flags & __SWR && fp->_p != NULL)

   127     {

   128       /*

   129        * Writing.  Any buffered characters cause the

   130        * position to be greater than that in the

   131        * underlying object.

   132        */

   133       pos += fp->_p - fp->_bf._base;

   134     }

   135 

   136   return pos;

   137 }