gets.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.
//
//  gets.c
//

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

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


char *gets(char *s)
{
  // gets() reads a line from stdin into the buffer pointed to by s until
  // either a terminating newline or EOF, which it replaces with '\0'.
  // No check for buffer overrun is performed.
  
  // The algorithm is to run in a loop until a newline or EOF is encountered.
  // Since we are reading from the text input stream, we need to continually
  // check whether there is any input before we call to get the character. 
  // If there is no input, yield the current time slice back to the
  // scheduler.

  int status = 0;
  int read = 0;
  char c = '\0';

  if (visopsys_in_kernel)
    {
      errno = ERR_BUG;
      return (NULL);
    }

  while(1)
    {
      // Is there anything in the input stream?
      if (!textInputCount())
	{
	  // Nothing to process.  Yield.
	  multitaskerYield();
	  continue;
	}

      // Always terminate with NULL
      s[read] = NULL;

      // Get a character from the text input stream
      status = textInputGetc(&c);
      if (status < 0)
	{
	  errno = status;
	  return (NULL);
	}

      // We have a character.

      // Is it an EOF or newline?  That would mean we're finished
      if ((c == EOF) || (c == '\n'))
	{
	  textNewline();

	  if (read == 0)
	    return (NULL);
	  else
	    return (s);
	}

      // It's some other character.  Copy it into the target string.
      else
	{
	  s[read++] = c;
	  textPutc(c);
	  continue;
	}
    }
}