Sponsored Content
Top Forums Programming what would happen if a process wrote to its own stdin? Post 302302042 by c_d on Sunday 29th of March 2009 10:56:38 PM
Old 03-29-2009
Quote:
Originally Posted by Perderabo
It wrote to stdin, aka file descriptor 0. You can add:
close(1);
close(2);
in front of your "if" statement to help prove it.

In this case, the shell opened /dev/tty for reading and writing and made all three initial fd's point to it.

Try:
echo hello > file
./a.out < file
echo who knows | ./a.out

i tried the exercise you suggested on
Code:
#include<unistd.h>
#include<fcntl.h>

int main()
{

    close(STDOUT_FILENO);
    close(STDERR_FILENO);
    if((write(STDIN_FILENO,"arrgh!",6))==-1)
    {
        perror("error writing to file");
    }    

}

i get no output or error whatsoever
but when i perform the same exercise on my original code

i get
Code:
[c_d@localhost C scratchpad]$ ./a.out <file
error writing to file: Bad file descriptor
[c_d@localhost C scratchpad]$ echo watup | ./a.out
error writing to file: Bad file descriptor

Quote:
In this case, the shell opened /dev/tty for reading and writing and made all three initial fd's point to it.
i wanted to see that...but i m not able to make fcntl() work...
Code:
#include<unistd.h>
#include<fcntl.h>
#include<stdlib.h>

int main()
{
    int x=2,file,fd;
    
    if((file=open("fdvals",O_RDWR))==-1)
    {
        perror("error opening fdvals");
    }
    fd=fcntl(file,F_GETFD,0);
    printf("fd=%d",fd);
    fd=fcntl(STDOUT_FILENO,F_GETFD,0);
    printf("fd=%d",fd);
}

it tells fd=0fd=0 Smilie
 

10 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

what happen when changing Hostname?

I 'm using RH 7.2 Genome in the Network Configuration I change therer are two places one for static hostname for my machine and in DNS hostname I don't know what happen when restarting my PC when connecting using dialer I can't browse the Internet also I can't use sendmail .......Server timeout... (2 Replies)
Discussion started by: atiato
2 Replies

2. Programming

Any one can tell me how this happen?

The #1 Online Store for Louis Vuitton Replicas is: http://www.opichina.com.cn. We offer Louis Vuitton Replicas and more! Whatever you call it: LV Bags, LV Replicas, Louis Vuitton Fake, Louis Vuitton Knockoffs, Louis Vuitton Bag, Louis Vuitton Purse, Louis Vuitton Wallet, Louis Vuitton Shoes,... (10 Replies)
Discussion started by: jiangyanna
10 Replies

3. UNIX for Dummies Questions & Answers

What would happen if. . .

Hi, Could someone please tell me what would happen if the following were entered into the command line: rm -i /books/*.* rm /books/* Many thanks! (3 Replies)
Discussion started by: crispy
3 Replies

4. UNIX for Advanced & Expert Users

Unix ID deleted - What happen to process

I have an unix id (AIX system) which is used to run a couple of processes. They also write some log files into a file system (that is not in the home directory of the user id, but in different location). One bad day, the id was deleted accidentally. But the home directory, files and everything... (1 Reply)
Discussion started by: cmgreat
1 Replies

5. UNIX for Dummies Questions & Answers

whats happen when we create new user

hi frndz I wanna knw exatly what happen when we create new user... which directories are created ?? which files are modified ?? thanx.... (2 Replies)
Discussion started by: luckypower
2 Replies

6. AIX

How does ITIL processing happen in AIX?

How does ITIL process is implemened in AIX? (6 Replies)
Discussion started by: AIXlearner
6 Replies

7. UNIX for Dummies Questions & Answers

What Does Happen During Boot Process? - BIOS and MBR

I'm talking about boot process in multi-boot Linux perceptive. Please tell me whether my explanation is right or wrong? If wrong, please explain. "The BIOS checks the system and loads this initial bootstrapping code into memory. This initial bootstrap code searches for an active partition... (0 Replies)
Discussion started by: f.ben.isaac
0 Replies

8. UNIX for Advanced & Expert Users

Who actually wrote Professional Linux Programming ?

Hello, Who actually wrote Professional Linux Programming of Wrox publication as there are two different sets of writers, one set consists of Jon Masters and Richard Blum and another set of writers is Neil Mathew with lots of other writers. Plz resolve it. I'm really confused. Regards.. (0 Replies)
Discussion started by: vectrum
0 Replies

9. Shell Programming and Scripting

Crontab - wrote Simple Script but i cant work out how to play it at a certain time.

Hi everyone. Silly might be silly be I'm still new to bash. I'm trying to make an Alarm Clock for in the morning using my laptop i have wrote this Simple Script but i cant work out how to play it at a certain time. #!/bin/bash cd /home/josh/Music/Bruno_Mars/Hooligans/ cvlc... (8 Replies)
Discussion started by: jtsmith90
8 Replies

10. What is on Your Mind?

Ah, the AMIGA, (another poem I wrote in 2005).

Well I wrote this in 2005 and uploaded to AMINET.as a commemoration of a machine that is still in use today. It is now 29 years since this machne came into being. Phenominal and it is still being supported- WOW! My A1200 is on 24/7 and I use it to test code developed on AMIGA emulators... ... (0 Replies)
Discussion started by: wisecracker
0 Replies
ppmtosixel(1)						      General Commands Manual						     ppmtosixel(1)

NAME
ppmtosixel - convert a portable pixmap into DEC sixel format SYNOPSIS
ppmtosixel [-raw] [-margin] [ppmfile] DESCRIPTION
Reads a portable pixmap as input. Produces sixel commands (SIX) as output. The output is formatted for color printing, e.g. for a DEC LJ250 color inkjet printer. If RGB values from the PPM file do not have maxval=100, the RGB values are rescaled. A printer control header and a color assignment table begin the SIX file. Image data is written in a compressed format by default. A printer control footer ends the image file. OPTIONS
-raw If specified, each pixel will be explicitly described in the image file. If -raw is not specified, output will default to com- pressed format in which identical adjacent pixels are replaced by "repeat pixel" commands. A raw file is often an order of magni- tude larger than a compressed file and prints much slower. -margin If -margin is not specified, the image will be start at the left margin (of the window, paper, or whatever). If -margin is speci- fied, a 1.5 inch left margin will offset the image. PRINTING
Generally, sixel files must reach the printer unfiltered. Use the lpr -x option or cat filename > /dev/tty0?. BUGS
Upon rescaling, truncation of the least significant bits of RGB values may result in poor color conversion. If the original PPM maxval was greater than 100, rescaling also reduces the image depth. While the actual RGB values from the ppm file are more or less retained, the color palette of the LJ250 may not match the colors on your screen. This seems to be a printer limitation. SEE ALSO
ppm(5) AUTHOR
Copyright (C) 1991 by Rick Vinci. 26 April 1991 ppmtosixel(1)
All times are GMT -4. The time now is 09:33 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy