ftell.c

上一个上传的有问题,这个是好的。visopsys包括系统内核和GUI的全部SOURCE code ,还包括一些基本的docs文档。里面src子目录对应所有SOURCE code.对于想研究操作系统的朋

// 
//  Visopsys
//  Copyright (C) 1998-2007 J. Andrew McLaughlin
//  
//  This library is free software; you can redistribute it and/or modify it
//  under the terms of the GNU Lesser General Public License as published by
//  the Free Software Foundation; either version 2.1 of the License, or (at
//  your option) any later version.
//
//  This library is distributed in the hope that it will be useful, but
//  WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
//  General Public License for more details.
//
//  You should have received a copy of the GNU Lesser General Public License
//  along with this library; if not, write to the Free Software Foundation,
//  Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
//
//  ftell.c
//

// This is the standard "ftell" function, as found in standard C libraries

#include <stdio.h>
#include <errno.h>
#include <sys/api.h>


long ftell(FILE *theStream)
{
  // The ftell() function obtains the current value of the file-position
  // indicator for the stream pointed to by stream.  Upon successful
  // completion, the ftell() function returns the current value of the
  // file-position indicator for the stream measured in bytes from the
  // beginning of the file.  Otherwise, they return -1 and sets errno to
  // indicate the error.

  // This call is not applicable for stdin, stdout, and stderr
  if ((theStream == stdin) || (theStream == stdout) || (theStream == stderr))
    return (errno = ERR_NOTAFILE);

  return ((theStream->block * theStream->f.blockSize) + theStream->s.last);
}