[Bug c++/30860] New: Should warn about boolean constant false used in pointer context

[Bug c++/30860] New: Should warn about boolean constant false used in pointer context

[rguenth at gcc dot gnu dot org]

void foo(const char *); 
void bar() { foo(false); }

should warn that 'false' is interpreted as NULL pointer constant and as such
is convertible to const char *.  (Through false -> (int)0 -> NULL -> (const
char *)0)

As foo(true) is (rightfully) rejected the case above is usually not intended.

See 4.10.


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           Summary: Should warn about boolean constant false used in pointer
                    context
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: enhancement
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30860

[Bug c++/30860] Should warn about boolean constant false used in pointer context

[mueller at gcc dot gnu dot org]

------- Comment #1 from mueller at gcc dot gnu dot org  2007-02-19 16:43 -------
manu, is this something already covered by your pending -Wconversion fixes?


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mueller at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30860

[Bug c++/30860] Should warn about boolean constant false used in pointer context

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2007-02-19 19:01 -------
I don't see why we should warn about a very valid and well defined and will
always work on every compiler.  You want to warn about a specific coding style
which I think is wrong in this case (and in the -Weffc++ case).


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30860

[Bug c++/30860] Should warn about boolean constant false used in pointer context

[manu at gcc dot gnu dot org]

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------- Comment #3 from manu at gcc dot gnu dot org  2007-02-19 19:14 -------
(In reply to comment #1)
> manu, is this something already covered by your pending -Wconversion fixes?
> 

No, it is not. And I don't think it should be warned by -Wconversion. After
all, no value is changed during the conversion. 

On the other hand, we give an error for:

void foo(const char *); 
void bar() { foo(1 != 0); }

error: cannot convert ‘bool’ to ‘const char*’ for argument ‘1’ to
‘void foo(const char*)’


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30860

[Bug c++/30860] Should warn about boolean constant false used in pointer context

[gdr at cs dot tamu dot edu]

------- Comment #4 from gdr at cs dot tamu dot edu  2007-02-19 19:48 -------
Subject: Re:  Should warn about boolean constant false used in pointer context

"pinskia at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> writes:

| I don't see why we should warn about a very valid and well defined and will
| always work on every compiler.  You want to warn about a specific coding
style
| which I think is wrong in this case (and in the -Weffc++ case).

The code may be well-formed C++, but it certainly is a candidate for
either a conceptual error (or typo) or part of obfuscated code contest.  

-- Gaby


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30860

[Bug c++/30860] Should warn about boolean constant false used in pointer context

[gdr at cs dot tamu dot edu]

------- Comment #5 from gdr at cs dot tamu dot edu  2007-02-19 19:59 -------
Subject: Re:  Should warn about boolean constant false used in pointer context

"manu at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> writes:

| No, it is not. And I don't think it should be warned by -Wconversion. After
| all, no value is changed during the conversion. 

Well, it appears to me that -Wconversion would be appropriate.

-- Gaby


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30860

[Bug c++/30860] Should warn about boolean constant false used in pointer context

[mueller at gcc dot gnu dot org]

-- 

mueller at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-02-19 20:21:31
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30860

[Bug c++/30860] Should warn about boolean constant false used in pointer context

[mueller at gcc dot gnu dot org]

------- Comment #6 from mueller at gcc dot gnu dot org  2007-02-19 20:23 -------
there is an implicit value conversion, boolean "false" to address "0". I think
that is the definition of -Wconversion, no?

anyway, I'll work on a patch. 


-- 

mueller at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |mueller at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30860

[Bug c++/30860] Should warn about boolean constant false used in pointer context

[gdr at cs dot tamu dot edu]

------- Comment #7 from gdr at cs dot tamu dot edu  2007-02-19 20:49 -------
Subject: Re:  Should warn about boolean constant false used in pointer context

"mueller at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> writes:

| there is an implicit value conversion, boolean "false" to address "0". I
think
| that is the definition of -Wconversion, no?

Yes.

-- Gaby


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30860

[Bug c++/30860] Should warn about boolean constant false used in pointer context

[manu at gcc dot gnu dot org]

------- Comment #8 from manu at gcc dot gnu dot org  2007-02-19 20:50 -------
(In reply to comment #6)
> there is an implicit value conversion, boolean "false" to address "0". I think
> that is the definition of -Wconversion, no?
> 
> anyway, I'll work on a patch. 
> 

Take a look at http://gcc.gnu.org/ml/gcc-patches/2007-02/txt00054.txt and
particularly at cp/call.c (convert_like_real). I think the warning should go
there with the other NULL warnings.

Cheers,

Manuel.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30860

[Bug c++/30860] Should warn about boolean constant false used in pointer context

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2007-02-20 09:53 -------
In reply to comment #4

The case that made me file this bug is changed overload resolution for a
false argument vs. a true argument.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30860

[Bug c++/30860] Should warn about boolean constant false used in pointer context

[mueller at gcc dot gnu dot org]

------- Comment #10 from mueller at gcc dot gnu dot org  2007-03-14 23:17 -------
Subject: Bug 30860

Author: mueller
Date: Wed Mar 14 23:17:03 2007
New Revision: 122934

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=122934
Log:
2007-03-15  Dirk Mueller  <dmueller@suse.de>

        PR c++/30860
        * call.c (convert_conversion_warnings): New..
        (convert_like_real): .. factored out from here.
        (convert_conversion_warnings): Add warning about
        false being converted to NULL in argument passing.

        * g++.dg/warn/Wconversion2.C: New.


Added:
    trunk/gcc/testsuite/g++.dg/warn/Wconversion2.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c
    trunk/gcc/testsuite/ChangeLog


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30860

[Bug c++/30860] Should warn about boolean constant false used in pointer context

[mueller at gcc dot gnu dot org]

------- Comment #11 from mueller at gcc dot gnu dot org  2007-03-14 23:20 -------
Fixed for 4.3.


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mueller at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30860