[Bug c++/31755] New: Clarify NULL pointer conversion to other types in initialiser

[Bug c++/31755] New: Clarify NULL pointer conversion to other types in initialiser

[jg at jguk dot org]

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Could the warning message below be revised to include a warning that NULL will
evaluate to false or zero?

In addition, is there a way to add the member name which is being initialised
to the warning? The line numbers are not accurate too, so it needs some
inspection to figure out the members concerned.

$ g++ -Wall -o t main.cpp
main.cpp: In constructor ‘A::A()’:
main.cpp:16: warning: converting to non-pointer type ‘bool’ from NULL
main.cpp:16: warning: converting to non-pointer type ‘int’ from NULL
main.cpp:16: warning: converting to non-pointer type ‘unsigned int’ from NULL


Could it be revised to display something like this?

$ g++ -Wall -o t main.cpp
main.cpp: In constructor ‘A::A()’:
main.cpp:16: warning: initialization of A::m_bool converts to non-pointer type
‘bool’ from NULL
main.cpp:16: warning: initialization of A::m_int converts to non-pointer type
‘int’ from NULL
main.cpp:16: warning: initialization of A::m_unit converts to non-pointer type
‘unsigned int’ from NULL



Example program:
=====================
// g++ -Wall -o t main.cpp
#include <string.h>

class A
{
        public:
        A();
        bool m_bool;
        int m_int;
        unsigned int m_uint;
};

A::A()
: m_bool(NULL),
m_int(NULL),
m_uint(NULL)
{
}

int main()
{       
}


-- 
           Summary: Clarify NULL pointer conversion to other types in
                    initialiser
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jg at jguk dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31755

[Bug c++/31755] Clarify NULL pointer conversion to other types in initialiser

[redi at gcc dot gnu dot org]

------- Comment #1 from redi at gcc dot gnu dot org  2009-12-08 23:29 -------
(In reply to comment #0)
> Could the warning message below be revised to include a warning that NULL will
> evaluate to false or zero?

What else would it evaluate to?

N.B. with recent versions of GCC -Wconversion is needed and the conversion to
bool no longer warns


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31755

[Bug c++/31755] Clarify NULL pointer conversion to other types in initialiser

[jg at jguk dot org]

------- Comment #2 from jg at jguk dot org  2010-02-14 12:34 -------

(In reply to comment #1)
> (In reply to comment #0)
> > Could the warning message below be revised to include a warning that NULL will
> > evaluate to false or zero?
> 
> What else would it evaluate to?

In C++ NULL is defined as 0, or 0L. However, as it is a special keyword, I
would like g++ to identify that it is special, and warn when initialising non
pointer types to be NULL.


> N.B. with recent versions of GCC -Wconversion is needed and the conversion to
> bool no longer warns

Ah ok, so it does this already, with the -Wconversion.. I had expected that
would be in -Wall!  Can it be added to -Wall?

Jon


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31755

[Bug c++/31755] Clarify NULL pointer conversion to other types in initialiser

[manu at gcc dot gnu dot org]

------- Comment #3 from manu at gcc dot gnu dot org  2010-02-14 20:04 -------
(In reply to comment #2)
> In C++ NULL is defined as 0, or 0L. However, as it is a special keyword, I
> would like g++ to identify that it is special, and warn when initialising non
> pointer types to be NULL.

This is on purpose. See PR c++/24745.

> Ah ok, so it does this already, with the -Wconversion.. I had expected that
> would be in -Wall!  Can it be added to -Wall?

No, it can't. Wconversion is too noisy at the moment and it warns for perfectly
legitimate code that is difficult to change. I think it is to imprecise even
for -Wextra.

http://gcc.gnu.org/wiki/NewWconversion

Since there is another bug for the other issues you mention, I am closing this
one as INVALID.


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu dot org
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31755