fgetpos.c

来自「标准c库代码,可以应用于各个系统提供了大量的基本函数」· C语言 代码 · 共 62 行

/*
FUNCTION
<<fgetpos>>---record position in a stream or file

INDEX
	fgetpos

ANSI_SYNOPSIS
	#include <stdio.h>
	int fgetpos(FILE *<[fp]>, fpos_t *<[pos]>);

TRAD_SYNOPSIS
	#include <stdio.h>
	int fgetpos(<[fp]>, <[pos]>)
	FILE *<[fp]>;
	fpos_t *<[pos]>;

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.

You can use <<fgetpos>> to report on the current position for a file
identified by <[fp]>; <<fgetpos>> will write a value
representing that position at <<*<[pos]>>>.  Later, you can
use this value with <<fsetpos>> to return the file to this
position.

In the current implementation, <<fgetpos>> simply uses a character
count to represent the file position; this is the same number that
would be returned by <<ftell>>.

RETURNS
<<fgetpos>> returns <<0>> when successful.  If <<fgetpos>> fails, the
result is <<1>>.  Failure occurs on streams that do not support
positioning; the global <<errno>> indicates this condition with the
value <<ESPIPE>>.

PORTABILITY
<<fgetpos>> is required by the ANSI C standard, but the meaning of the
value it records is not specified beyond requiring that it be
acceptable as an argument to <<fsetpos>>.  In particular, other
conforming C implementations may return a different result from
<<ftell>> than what <<fgetpos>> writes at <<*<[pos]>>>.

No supporting OS subroutines are required.
*/

#include <stdio.h>

int
_DEFUN (fgetpos, (fp, pos),
	FILE * fp _AND
	fpos_t * pos)
{
  *pos = ftell (fp);

  if (*pos != -1)
    return 0;
  return 1;
}