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检测重定向
类型: Sample Code (HOWTO)	类别: Other
许可证: GNU General Public License	语言: C
描述: 显示怎样检测stdin, stdout, stderr是否被重定向。

该代码片段的版本系列:

片段ID	下载版本	提交时间	提交人	删除
2	0.1	2001-07-24 10:49	bbsadmin

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最新版本的代码片段: 0.1

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

/* -------------------------------------------------------------- 

  detecting_redirection
  
  Part of the SourceLib Project at LinuxProgramming.com
  http://linuxprogramming.com/SourceLib

  This sample program has been released into the public domain.

  Purpose: Detect, separately, whether stdin, stdout, and
  stderr have been redirected or are connected to a real terminal.

  Use the command "make" to build this program, and then "make
  stdin", "make stdout", or "make stderr" to test it by redirecting
  each one.

  ---------------------------------------------------------------

  All our program does is display our ever friendly message and
  terminate normally.  

  --------------------------------------------------------------- */

/* -------------------------------------------------------------
   This function prints the two strings passed to it, separated 
   by a blank, to either stdout or stderr, depending on the value 
   of the flag use_stdout.
   ------------------------------------------------------------- */

void emit(char *device_name, char *message_text, int use_stdout)
{
  if(use_stdout)
    printf("%s %s",device_name,message_text);
  else
    fprintf(stderr,"%s %s",device_name,message_text);
}

/* -------------------------------------------------------------
   This function does the real work in this sample, as it uses 
   the isatty() function to check if the system file (which is
   specified by its file number) is redirected, and then uses
   the emit() function to tell the world about what it found.
   ------------------------------------------------------------- */

void reportOnDevice(int file_number, char *device_name, int use_std_out)
{
  if(isatty(file_number) == 1)
    emit(device_name,"is connected to a terminal.\n",use_std_out);
  else
    emit(device_name,"is NOT connected to terminal.\n",use_std_out);
}

/* ------------------------------------------------------------- 
   The main program sets the use_stdout flag to indicate how 
   emit() should display text.  This prevents text from being 
   redirected into a file when we'd prefer to see it on the screen.

   We then use reportOnDevice() to check stdin, stdout, and 
   stderr.
   ------------------------------------------------------------- */

int main(int argc, char **argv)
{
  int use_stdout = 1;

  if(isatty(STDOUT_FILENO) != 1)
    use_stdout = 0;

  emit("","----------------------------------------------\n\n",use_stdout);

  reportOnDevice(STDIN_FILENO,"stdin",use_stdout);
  reportOnDevice(STDOUT_FILENO,"stdout",use_stdout);
  reportOnDevice(STDERR_FILENO,"stderr",use_stdout);

  emit("","\n\n",use_stdout);

  /* Indicate normal termination via the 
     EXIT_SUCCESS constant from stdlib.h */

  return EXIT_SUCCESS;
}


		

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