[Bug c/24971] New: missing prototype causes strange effect at a distance with float.

[Bug c/24971] New: missing prototype causes strange effect at a distance with float.

[hansen at cmu dot edu]

(972) uname -a
FreeBSD gadoid.ices.cmu.edu 5.2.1-RELEASE FreeBSD 5.2.1-RELEASE #0: Mon Feb 23
20:45:55 GMT 2004     root@wv1u.btc.adaptec.com:/usr/obj/usr/src/sys/GENERIC 
i386
(973) cat a.c
#include <stdlib.h>
#include <stdio.h>

int main(int argc,char *argv[])
{
  float n = 40;
  int i;

  for (i = 0;i < 10;i++)
    foo();

  printf("%g\n",n + 2.0);
  return 0;
}

float foo()
{
  return 1.0;
}
(974) gcc a.c -o a
a.c:17: warning: type mismatch with previous implicit declaration
a.c:10: warning: previous implicit declaration of `foo'
a.c:17: warning: `foo' was previously implicitly declared to return `int'
(975) ./a
nan
(976) 

The above program is missing a prototype for the "foo" function.  This
correctly causes a warning, but the missing prototype causes problems for
completely unrelated code.  In the above example, the foo() function is called
10 times, then an unrelated floating point operation is peformed which
incorrectly results in a "nan".  Note that if the number of loop iterations is
reduced to 6 or fewer times, the program will print the correct result.


-- 
           Summary: missing prototype causes strange effect at a distance
                    with float.
           Product: gcc
           Version: 3.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hansen at cmu dot edu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24971

[Bug c/24971] missing prototype causes strange effect at a distance with float.

[pinskia at gcc dot gnu dot org]

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------- Comment #2 from pinskia at gcc dot gnu dot org  2005-11-21 15:16 -------
Note the error is:
t.c:17: error: conflicting types for ‘foo’
t.c:10: error: previous implicit declaration of ‘foo’ was here


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24971

[Bug c/24971] missing prototype causes strange effect at a distance with float.

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2005-11-21 15:16 -------
This code should have been rejected as it is for 3.4.0 and above.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
           Keywords|                            |accepts-invalid
         Resolution|                            |FIXED
   Target Milestone|---                         |3.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24971

[Bug c/24971] missing prototype causes strange effect at a distance with float.

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2005-11-21 15:18 -------
*** Bug 24972 has been marked as a duplicate of this bug. ***


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24971

[Bug c/24971] missing prototype causes strange effect at a distance with float.

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2005-11-21 15:18 -------
*** Bug 24973 has been marked as a duplicate of this bug. ***


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24971

[Bug c/24971] missing prototype causes strange effect at a distance with float.

[hansen at cmu dot edu]

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------- Comment #5 from hansen at cmu dot edu  2005-11-21 15:28 -------
(In reply to comment #2)
> Note the error is:
> t.c:17: error: conflicting types for ‘foo’
> t.c:10: error: previous implicit declaration of ‘foo’ was here
> 

I only get warnings in 3.3.0.  Even with warnings, I still do not think that
there should be an effect in code unrelated to the warning.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24971