Styjun

Like totally amazing interchangeable sister outfit accessory swapping or whatever

xkeyval -- read keys from file

Lights are flickering on and off after accidentally bumping into light switch

Why does my GNOME settings mention "Moto C Plus"?

When speaking, how do you change your mind mid-sentence?

What is the evidence that custom checks in Northern Ireland are going to result in violence?

Converting a text document with special format to pandas data frame

Does using the inspiration rules for character defects tend to encourage players to display MGS?

Can I ask an author to send me his ebook?

Does GDPR cover the collection of data by websites that crawl the web and resell user data

Should man-made satellites feature an intelligent inverted "cow catcher"?

What's the connection between Mr. Nancy and fried chicken?

Network Switch Upgrade Planning questions

Is Bran literally the world's memory?

Why do C and C++ allow the expression (int) + 4*5?

Reflections in a Square

Why "Go Out and Learn"

Assertions In A Mock Callout Test

Raising a bilingual kid. When should we introduce the majority language?

Can Deduction Guide have an explicit(bool) specifier?

Can this water damage be explained by lack of gutters and grading issues?

Can I take recommendation from someone I met at a conference?

How to get a single big right brace?

Import keychain to clean macOS install?

in c system() executes before printf() even when printf come first [duplicate]

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty height:90px;width:728px;box-sizing:border-box;

2

0

This question already has an answer here:

• 
  C/Unix Strange behaviour while using system calls and printf
  
  1 answer
  
  

I just started using the system() function in c, and I thought of starting the same executable from within it self using the system function, so I wrote the following program

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

int main()

 printf("some string");
 system("./a.out");

-I used gcc to compile it-

when I ran the program it did not print anything, it just kept going until I used the shortcut ctrl-c to stop the execution,then it started printing the output(it did not print anything until I stopped it)

I believe the statements should execute sequentially, why did it not print anything until I stopped it?

c linux gcc

share|improve this question

asked Mar 22 at 14:00

BlueBlue

132

marked as duplicate by phuclv, Jens Gustedt c
Users with the  c badge can single-handedly close c questions as duplicates and reopen them as needed.

StackExchange.ready(function()
if (StackExchange.options.isMobile) return;

$('.dupe-hammer-message-hover:not(.hover-bound)').each(function()
var $hover = $(this).addClass('hover-bound'),
$msg = $hover.siblings('.dupe-hammer-message');

$hover.hover(
function()
$hover.showInfoMessage('',
messageElement: $msg.clone().show(),
transient: false,
position: my: 'bottom left', at: 'top center', offsetTop: -7 ,
dismissable: false,
relativeToBody: true
);
,
function()
StackExchange.helpers.removeMessages();

);
);
);
Mar 22 at 15:50

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  system is using fork under the hood. And the output of printf is buffered and can get flushed at any moment - before or after executing the child. Flush it explicitly by adding n or usng fflush(stdout) if the order is important..
  
  – Eugene Sh.
  Mar 22 at 14:03
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  The output stream is buffered, so the text you print may not appear until you flush the stream or the process exits.
  
  – Krzysiek Karbowiak
  Mar 22 at 14:05
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ty for the explanation.
  
  – Blue
  Mar 22 at 14:09
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  printf anomaly after "fork()", why does "printf" not work?
  
  – phuclv
  Mar 22 at 15:20
  

  
  
  
  

add a comment | 

2

0

This question already has an answer here:

• 
  C/Unix Strange behaviour while using system calls and printf
  
  1 answer
  
  

I just started using the system() function in c, and I thought of starting the same executable from within it self using the system function, so I wrote the following program

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

int main()

 printf("some string");
 system("./a.out");

-I used gcc to compile it-

when I ran the program it did not print anything, it just kept going until I used the shortcut ctrl-c to stop the execution,then it started printing the output(it did not print anything until I stopped it)

I believe the statements should execute sequentially, why did it not print anything until I stopped it?

c linux gcc

share|improve this question

asked Mar 22 at 14:00

BlueBlue

132

marked as duplicate by phuclv, Jens Gustedt c
Users with the  c badge can single-handedly close c questions as duplicates and reopen them as needed.

StackExchange.ready(function()
if (StackExchange.options.isMobile) return;

$('.dupe-hammer-message-hover:not(.hover-bound)').each(function()
var $hover = $(this).addClass('hover-bound'),
$msg = $hover.siblings('.dupe-hammer-message');

$hover.hover(
function()
$hover.showInfoMessage('',
messageElement: $msg.clone().show(),
transient: false,
position: my: 'bottom left', at: 'top center', offsetTop: -7 ,
dismissable: false,
relativeToBody: true
);
,
function()
StackExchange.helpers.removeMessages();

);
);
);
Mar 22 at 15:50

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  system is using fork under the hood. And the output of printf is buffered and can get flushed at any moment - before or after executing the child. Flush it explicitly by adding n or usng fflush(stdout) if the order is important..
  
  – Eugene Sh.
  Mar 22 at 14:03
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  The output stream is buffered, so the text you print may not appear until you flush the stream or the process exits.
  
  – Krzysiek Karbowiak
  Mar 22 at 14:05
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ty for the explanation.
  
  – Blue
  Mar 22 at 14:09
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  printf anomaly after "fork()", why does "printf" not work?
  
  – phuclv
  Mar 22 at 15:20
  

  
  
  
  

add a comment | 

This question already has an answer here:

• 
  C/Unix Strange behaviour while using system calls and printf
  
  1 answer
  
  

I just started using the system() function in c, and I thought of starting the same executable from within it self using the system function, so I wrote the following program

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

int main()

 printf("some string");
 system("./a.out");

-I used gcc to compile it-

when I ran the program it did not print anything, it just kept going until I used the shortcut ctrl-c to stop the execution,then it started printing the output(it did not print anything until I stopped it)

I believe the statements should execute sequentially, why did it not print anything until I stopped it?

c linux gcc

share|improve this question

asked Mar 22 at 14:00

BlueBlue

132

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

int main()

 printf("some string");
 system("./a.out");

share|improve this question

asked Mar 22 at 14:00

BlueBlue

132

share|improve this question

asked Mar 22 at 14:00

BlueBlue

132

asked Mar 22 at 14:00

BlueBlue

132

asked Mar 22 at 14:00

BlueBlue

132

1 Answer
1

active

oldest

votes

5

By default, when stdoutis connected to a terminal, it is line-buffered.

printf("some string");

doesn't have a 'n' in it and you aren't calling fflush(stdout); after it either, so all this printf("some string"); does is copy "some string" into your stdout's output buffer.

The buffer is flushed as the end of main.

printf("some stringn"); would flush the buffer immediately, provided stdout is connected to a terminal and you didn't change stdout's buffering.

printf("some string"); fflush(stdout); will flush the buffer immediately regardless of context and without the need for the 'n'.

share|improve this answer

edited Mar 22 at 14:14

answered Mar 22 at 14:04

PSkocikPSkocik

35.8k65580

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think it is important to explain why the output reordering it is happening with system but not with some other functions.
  
  – Eugene Sh.
  Mar 22 at 14:22
  

  
  
  
  

add a comment | 

5

By default, when stdoutis connected to a terminal, it is line-buffered.

printf("some string");

doesn't have a 'n' in it and you aren't calling fflush(stdout); after it either, so all this printf("some string"); does is copy "some string" into your stdout's output buffer.

The buffer is flushed as the end of main.

printf("some stringn"); would flush the buffer immediately, provided stdout is connected to a terminal and you didn't change stdout's buffering.

printf("some string"); fflush(stdout); will flush the buffer immediately regardless of context and without the need for the 'n'.

share|improve this answer

edited Mar 22 at 14:14

answered Mar 22 at 14:04

PSkocikPSkocik

35.8k65580

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think it is important to explain why the output reordering it is happening with system but not with some other functions.
  
  – Eugene Sh.
  Mar 22 at 14:22
  

  
  
  
  

add a comment | 

5

By default, when stdoutis connected to a terminal, it is line-buffered.

printf("some string");

doesn't have a 'n' in it and you aren't calling fflush(stdout); after it either, so all this printf("some string"); does is copy "some string" into your stdout's output buffer.

The buffer is flushed as the end of main.

printf("some stringn"); would flush the buffer immediately, provided stdout is connected to a terminal and you didn't change stdout's buffering.

printf("some string"); fflush(stdout); will flush the buffer immediately regardless of context and without the need for the 'n'.

share|improve this answer

edited Mar 22 at 14:14

answered Mar 22 at 14:04

PSkocikPSkocik

35.8k65580

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think it is important to explain why the output reordering it is happening with system but not with some other functions.
  
  – Eugene Sh.
  Mar 22 at 14:22
  

  
  
  
  

add a comment | 

By default, when stdoutis connected to a terminal, it is line-buffered.

printf("some string");

doesn't have a 'n' in it and you aren't calling fflush(stdout); after it either, so all this printf("some string"); does is copy "some string" into your stdout's output buffer.

The buffer is flushed as the end of main.

printf("some stringn"); would flush the buffer immediately, provided stdout is connected to a terminal and you didn't change stdout's buffering.

printf("some string"); fflush(stdout); will flush the buffer immediately regardless of context and without the need for the 'n'.

share|improve this answer

edited Mar 22 at 14:14

answered Mar 22 at 14:04

PSkocikPSkocik

35.8k65580

printf("some string");

share|improve this answer

edited Mar 22 at 14:14

answered Mar 22 at 14:04

PSkocikPSkocik

35.8k65580

answered Mar 22 at 14:04

PSkocikPSkocik

35.8k65580

answered Mar 22 at 14:04

PSkocikPSkocik

35.8k65580