Sender: dscott AT chernikeeff DOT co DOT uk
Message-Id: <3649ECBC.794BDF32@chernikeeff.co.uk>
Date: Wed, 11 Nov 1998 19:59:56 +0000
From: Doug Scott <dscott AT chernikeeff DOT co DOT uk>
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To: djgpp AT delorie DOT com
Subject: gcc v281 bug?
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Reply-To: djgpp AT delorie DOT com

Hi,

I am not a compiler wizard but I think that I have found a bug in djgpp.


Versions:
	bnu281b
	djdev201
	gcc281b
	operating system NT 4.0 SP3

The Code:

#include <stdio.h>
main( int argc, char* argv[] ) 
{
        printf( "aaa" ) ;
        putch( 'Q' ) ;          /* goes to screen not stdout */
        printf ( "zzz") ;
}


Compiled with:
	gcc test1.c -o test1.exe -lm

The output is:
Qaaazzz

I would expect the output to be:
aaaQzzz

Other notes:
If the program is run with 

	test1 > out

The character Q goes to the screen and the rest to the file.
I cannot recall  if putch() is "supposed to" use stdout or not and I
have mentioned this here just in case it is.


I also tried outputting many (1000) Q's with a for loop and the order
was the same. That is Q's first.
Code fragment for this:
        printf( "aaa" ) ;
	for ( i=0 ; i<1000 ; i++ )
	        putch( 'Q' ) ;     /* goes to screen not stdout */
        printf ( "zzz") ;

This latter test result suggests to me that the problem may be due to
some code re-ordering due to optimisation, and not as I at first
considered due to NT returning from printf() before the output was
actually put on the display and putch() taking a shortcut and getting
there first.

I do not read the mail list but it would be nice to know if the bug is
in my analysis or in the compiler/library. 


Douglas.