[Bug c/46672] New: Problem with fork and buffer

[Bug c/46672] New: Problem with fork and buffer

[debayanin at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46672

           Summary: Problem with fork and buffer
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: debayanin@gmail.com


I typed the following program on my machine:

#include <stdio.h>

int main()
{
 printf("Hello");
 fork();
 printf("World");
}

The output I get is: HelloWorldHelloWorld

I then change line number 5:

#include <stdio.h>

int main()
{
 printf("Hello\n");
 fork();
 printf("World");
}

The output becomes: 

Hello
WorldWorld


So in effect adding a \n eats up a Hello\n as well.
I think this is a bug, but not sure where.

[Bug c/46672] Problem with fork and buffer

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46672

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2010-11-26 10:28:58 UTC ---
Concurrent writes to stdout (any files) invoke undefined behavior.

[Bug c/46672] Problem with fork and buffer

[debayanin at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46672

Debayan Banerjee <debayanin at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |

--- Comment #2 from Debayan Banerjee <debayanin at gmail dot com> 2010-11-26 10:44:45 UTC ---
(In reply to comment #1)
> Concurrent writes to stdout (any files) invoke undefined behavior.

I dont think its undefined. For my compiler it always produces this output. I
tried the same on http://ideone.com (dont know which compiler they are using)
and it prints the correct output.

Also, doesnt each process have its own stdout?

[Bug c/46672] Problem with fork and buffer

[schwab@linux-m68k.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46672

Andreas Schwab <schwab@linux-m68k.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #3 from Andreas Schwab <schwab@linux-m68k.org> 2010-11-26 10:51:06 UTC ---
There is nothing lost.  If stdout is line buffered then \n forces a flush.

[Bug c/46672] Problem with fork and buffer

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46672

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu.org

--- Comment #4 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2010-11-26 11:05:56 UTC ---
Undefined: http://c-faq.com/ansi/undef.html