[Bug c/27646] New: compiling very simple flex generated code results in global variabl error with GCC 4.0.1

[Bug c/27646] New: compiling very simple flex generated code results in global variabl error with GCC 4.0.1

[jesser at pixelworks dot com]

Hi,

My system is a macbook pro (intel duo core) with standard install of OS X.  GCC
version 4.01 Build 5250.

I am writing a flex program and ran across a very strange issue.  When building
and running the following flex (lex) program, the global variable access does
not work properly.  The expected output from this program (when the a character
is found) is :

glo = 5
5 = ret, glo = 5

but when building/running this program using GCC 4.01 , I get this output:

glo = 5
5 = ret, glo = 0

It works well with GCC v3.x

Here is the simple lex program:

%{
#include <stdio.h>

#define yywrap() 1

int glo;
%}

%%
"a"    { glo = 5;
         printf("glo = %d\n", glo);
         return (int)5;
       }
%%

main ()
{
    printf("%d = ret, glo = %d", yylex(), glo);
}

To build this, I am running:
flex test.l
gcc lex.yy.c

to run,
a.out

Then press the a key and enter.


-- 
           Summary: compiling very simple flex generated code results in
                    global variabl error with GCC 4.0.1
           Product: gcc
           Version: 4.0.1
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jesser at pixelworks dot com
 GCC build triplet: GCC version 4.0.1 build 5250
  GCC host triplet: MacBookPro OSX
GCC target triplet: MacBookPro OSX i686-apple-darwin8


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27646

[Bug c/27646] compiling very simple flex generated code results in global variabl error with GCC 4.0.1

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-05-17 19:06 -------
printf("%d = ret, glo = %d", yylex(), glo);

The C standard does not specify if yylex() or glo is evulated first.
So you are running into that effect and this is code undefined.

See PR 11751 for future reference.

*** This bug has been marked as a duplicate of 11751 ***


-- 

pinskia at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27646