pending/1590: Bug in structure???

[Yannick Copin <y dot copin at ipnl dot in2p3 dot fr>]

>Number:         1590
>Category:       pending
>Synopsis:       Bug in structure???
>Confidential:   yes
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          change-request
>Submitter-Id:   unknown
>Arrival-Date:   Mon Mar 22 21:18:01 UTC 2004
>Closed-Date:
>Last-Modified:
>Originator:     
>Release:        
>Organization:
>Environment:
>Description:
 Hi,
 
 sorry to bother you with probably a stupid question regarding gdb, but I 
   found a strange behavior in gdb 6.0 used along with gcc 3.3.2 (RedHat 
 7.2). Consider the following minimalist program:
 
 #define lg_name 80L
 
 typedef struct
 {
    char   name[lg_name+1];
    double step;
 } E3D_file;
 
 int main()
 {
    E3D_file cube;
 
    cube.step = 1.;
    return(0);
 }
 
 After standard compilation (gcc -g -Wall, version 3.3.2), gdb ./a.out gives:
 
 GNU gdb 6.0
 [...]
 (gdb) b main
 Breakpoint 1 at 0x80483a0: file testE3D.c, line 14.
 (gdb) r
 Starting program: /home/novae/ycopin/soft/c/tests/a.out
 
 Breakpoint 1, main () at testE3D.c:14
 14        cube.step = 1.;
 (gdb) display cube.step
 1: cube.step = 5.3440552952533551
 (gdb) n
 16        return(0);
 1: cube.step = 5.3440561285242438
 (gdb)
 17      }
 1: cube.step = 5.3440561285242438
 (gdb)
 Program exited normally.
 
 The 1st cube.step = 5.34 is normal, but after the initialization 
 cube.step = 1, I still got 5.34!!!
 
 This behavior doesnt show up with gcc 2.96 (RedHat):
 
 GNU gdb Red Hat Linux 7.x (5.0rh-15) (MI_OUT)
 
 Breakpoint 1, main () at testE3D.c:14
 14      cube.step = 1.;
 (gdb) display cube.step
 1: cube.step = -1.9967124462120234
 (gdb) n
 16      return(0);
 1: cube.step = 1
 
 but it's there with gcc 3.3 (instead of 3.3.2), and with gdb 5.3 and 
 5.2.1 (instead of 6.0).
 
 Furthermore, if I add a printf from the stdio lib, here is what I got 
 (gcc 3.3.2):
 
 Breakpoint 1, main () at testE3D.c:16
 16        printf("step (before) = %lf\n",cube.step);
 (gdb) display cube.step
 1: cube.step = 5.3440552952534404
 (gdb) n
 step (before) = 0.000000
 17        cube.step = 1.;
 1: cube.step = 5.3440552952534404
 (gdb) n
 18        printf("step (after) = %lf\n",cube.step);
 1: cube.step = 5.3440561285242438
 (gdb)
 step (after) = 1.000000
 20        return(0);
 1: cube.step = 5.3440561285242438
 
 The print-out via printf and the display of gdb don't give the same thing!!!
 
 Is it a bug in gdb (or gcc?), or is it just that I don't know how to use 
 it???
 
 Cheers.
 -- 
    .~.   Yannick COPIN  (o:>*  Doctus cum libro
    /V\   Institut de physique nucleaire de Lyon (IN2P3 - France)
   // \\  Tel: (33/0) 472 448 065
 /(   )\ http://snovae.in2p3.fr/ycopin/
   ^`~'^
 
 
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