[Bug c++/23194] New: Unhelpful diagnostic for incorrect pointer-to-member function syntax

[Bug c++/23194] New: Unhelpful diagnostic for incorrect pointer-to-member function syntax

[redi at gcc dot gnu dot org]

Given:

struct A {
    void mf() {}
};

int main()
{
    void (A::*pmf)() = &A::mf;
    A a;
    a.*pmf();   // should be (a.*pmf)();
}

mainline GCC says to use .* or ->* to use the PMF,

pfm_diag.cc: In function 'int main()':
pfm_diag.cc:9: error: must use '.*' or '->*' to call pointer-to-member function
in 'pmf (...)'

This is unhelpful if you don't know the right syntax, because the correct
operator _is_ present, but the compiler is complaining about the expression to
the right of the operator.  Maybe it would be better if the error message had a
complete example after it:

pfm_diag.cc: In function 'int main()':
pfm_diag.cc:9: error: must use '.*' or '->*' to call pointer-to-member function
in 'pmf (...)', e.g. '(a.*f) (...)'

-- 
           Summary: Unhelpful diagnostic for incorrect pointer-to-member
                    function syntax
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: redi at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-08-02 06:41 -------
Before 3.3, GCC gave:
t.cc:9: pointer to member function called, but not in class scope


Which is even worse.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
      Known to fail|                            |3.3 4.0.0 4.1.0 3.2.3 3.4.5
                   |                            |3.3.3 2.95.3
   Last reconfirmed|0000-00-00 00:00:00         |2005-08-02 06:41:48
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[redi at gcc dot gnu dot org]

------- Additional Comments From redi at gcc dot gnu dot org  2005-08-02 08:45 -------
Ah, I didn't check further back than 3.3, thanks, Andrew.

For comparison, Comeau's online compiler doesn't give a very helpful message
either, it says that "a.*pmf" must be an expression - which is true but no more
likely to help inexpert users realise that they need parentheses.



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[jwakely dot gcc at gmail dot com]

------- Comment #14 from jwakely dot gcc at gmail dot com  2008-06-24 20:46 -------
Fixed for 4.4


-- 

jwakely dot gcc at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[redi at gcc dot gnu dot org]

------- Comment #13 from redi at gcc dot gnu dot org  2008-06-24 20:44 -------
Subject: Bug 23194

Author: redi
Date: Tue Jun 24 20:44:04 2008
New Revision: 137086

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=137086
Log:
        PR c++/23194
        * typeck.c (cp_build_function_call): Show example syntax in
        diagnostic.

Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/typeck.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[jwakely dot gcc at gmail dot com]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
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------- Comment #12 from jwakely dot gcc at gmail dot com  2007-10-03 00:31 -------
I'm bootstrapping mainline as of yesterday (r128908) with gcc version 4.1.2
20070626 (Red Hat 4.1.2-13)

The format I tried was:
      error ("must use %<.*%> or %<->*%> to call pointer-to-member "
             "function in %<%1$E (...)%>, e.g. %<(... ->* %1$E) (...)%>",
             original);
and I get:
cc1: warnings being treated as errors
../../gcc-4.x/gcc/cp/typeck.c: In function ‘build_function_call’:
../../gcc-4.x/gcc/cp/typeck.c:2720: error: unknown conversion type character
‘1’ in format
../../gcc-4.x/gcc/cp/typeck.c:2720: error: unknown conversion type character
‘1’ in format
../../gcc-4.x/gcc/cp/typeck.c:2720: error: too many arguments for format


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[pinskia at gcc dot gnu dot org]

------- Comment #11 from pinskia at gcc dot gnu dot org  2007-10-03 00:24 -------
(In reply to comment #10)
> Andrew, unfortunately that format fails with -Werror

That should work, what version of GCC are you using to compile GCC?  If it does
not work, we forgot to add this formating checking to GCC itself even though we
added support for it (mostly for translations).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[jwakely dot gcc at gmail dot com]

------- Comment #10 from jwakely dot gcc at gmail dot com  2007-10-03 00:16 -------
Andrew, unfortunately that format fails with -Werror

I'm testing now, but my machine's developed a hardware problem and keeps
segfaulting, which makes it hard to build GCC let alone run the testsuite.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[bangerth at dealii dot org]

------- Comment #9 from bangerth at dealii dot org  2007-10-03 00:03 -------
Now we only need someone to test the patch and a diagnostic maintainer to
approve...


-- 

bangerth at dealii dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[jwakely dot gcc at gmail dot com]

------- Comment #8 from jwakely dot gcc at gmail dot com  2007-10-02 23:59 -------
Yes, it looks better with spaces, thanks.

I think ->* still looks clearer than .* even with the spaces.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

Re: [Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[Andrew Pinski]

On 2 Oct 2007 23:54:04 -0000, jwakely dot gcc at gmail dot com
<gcc-bugzilla@gcc.gnu.org> wrote:
> ------- Comment #6 from jwakely dot gcc at gmail dot com  2007-10-02 23:54 -------
> (From update of attachment 14287)
> >+           "function in %<%E (...)%>, e.g. %<(... ->* %E) (...)%>",
> >+           original, original);
> >       return error_mark_node;

It might be better to use %$1E (I think that is how it is done) so you
don't have to pass original twice.

Thanks,
Andrew Pinski

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[pinskia at gmail dot com]

------- Comment #7 from pinskia at gmail dot com  2007-10-02 23:59 -------
Subject: Re:  Unhelpful diagnostic for incorrect pointer-to-member function
syntax

On 2 Oct 2007 23:54:04 -0000, jwakely dot gcc at gmail dot com
<gcc-bugzilla@gcc.gnu.org> wrote:
> ------- Comment #6 from jwakely dot gcc at gmail dot com  2007-10-02 23:54 -------
> (From update of attachment 14287)
> >+           "function in %<%E (...)%>, e.g. %<(... ->* %E) (...)%>",
> >+           original, original);
> >       return error_mark_node;

It might be better to use %$1E (I think that is how it is done) so you
don't have to pass original twice.

Thanks,
Andrew Pinski


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[jwakely dot gcc at gmail dot com]

------- Comment #6 from jwakely dot gcc at gmail dot com  2007-10-02 23:54 -------
(From update of attachment 14287)
>Index: gcc/cp/typeck.c
>===================================================================
>--- gcc/cp/typeck.c	(revision 128908)
>+++ gcc/cp/typeck.c	(working copy)
>@@ -2716,8 +2716,8 @@
>   if (TYPE_PTRMEMFUNC_P (fntype))
>     {
>       error ("must use %<.*%> or %<->*%> to call pointer-to-member "
>-	     "function in %<%E (...)%>",
>-	     original);
>+	     "function in %<%E (...)%>, e.g. %<(... ->* %E) (...)%>",
>+	     original, original);
>       return error_mark_node;
>     }
> 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[bangerth at dealii dot org]

------- Comment #5 from bangerth at dealii dot org  2007-10-02 23:29 -------
(In reply to comment #4)

> I chose to use ->* not .* because otherwise you get (....*pmf) which doesn't
> help either!

You could leave a space around either of the two operators.

W.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[jwakely dot gcc at gmail dot com]

------- Comment #4 from jwakely dot gcc at gmail dot com  2007-10-02 23:28 -------
Created an attachment (id=14287)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14287&action=view)
add example to diagnostic

This adds ", e.g. '(...->*pmf) (...)'" to the error message.

I chose to use ->* not .* because otherwise you get (....*pmf) which doesn't
help either!


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194

[Bug c++/23194] Unhelpful diagnostic for incorrect pointer-to-member function syntax

[bangerth at dealii dot org]

------- Comment #3 from bangerth at dealii dot org  2007-10-02 22:08 -------
Still present. I know I should know better, but I too ran into this knife
just now and couldn't figure out what was going on for 10 minutes before I
remembered. The error message is really not very helpful...

W.


-- 

bangerth at dealii dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bangerth at dealii dot org
      Known to fail|3.3 4.0.0 4.1.0 3.2.3 3.4.5 |3.3 4.0.0 4.1.0 4.2.0 4.3.0
                   |3.3.3 2.95.3                |3.2.3 3.4.5 3.3.3 2.95.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23194