[Bug c++/30331] New: a const member function can call a non_const member function without const_cast

[Bug c++/30331] New: a const member function can call a non_const member function without const_cast

[hongleij at 126 dot com]

//const_test.cpp
struct A
{
  A(unsigned int n)
  {
     aa=n;        
  }
  void const_fun() const
  {
      static_cast<A>(*this).fun();  //ok
     // fun();       //err  
  }
  void fun()
  {
  }
  unsigned int aa;
};

int main()
{
    const A a(56);
    a.const_fun();
}

//  g++ const_test.cpp
//  ./a.out
//we should forbid call non_const member function  in a const member function
without an explicit const_cast ,isn't it?


-- 
           Summary: a const member function can call a non_const member
                    function without const_cast
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hongleij at 126 dot com
  GCC host triplet: all


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30331

[Bug c++/30331] a const member function can call a non_const member function without const_cast

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-12-30 08:08 -------
The following is ok:
      static_cast<A>(*this).fun();  //ok

Because you are creating a rvalue to hold "*this" which is then bound to a
const lvalue.

The following is an error:
      fun();       //err  
Because func is not a non_const.

Or I am missing something because all the versions of GCC I tried give an
error.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.0.1 4.2.0 4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30331

[Bug c++/30331] a const member function can call a non_const member function without const_cast

[gdr at integrable-solutions dot net]

------- Comment #2 from gdr at integrable-solutions dot net  2006-12-30 11:21 -------
Subject: Re:   New: a const member function can call a non_const member
function without const_cast

"hongleij at 126 dot com" <gcc-bugzilla@gcc.gnu.org> writes:

| //const_test.cpp
| struct A
| {
|   A(unsigned int n)
|   {
|      aa=n;        
|   }
|   void const_fun() const
|   {
|       static_cast<A>(*this).fun();  //ok

yes, as mandated by C++ semantics -- the static_cast creates a
new object to which fun() is applied.  That is OK.

|      // fun();       //err  

direct call to fun() is an error.

So, this PR does not report an error.  It should be closed as "mistaken".

-- Gaby


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30331

[Bug c++/30331] a const member function can call a non_const member function without const_cast

[hongleij at 126 dot com]

------- Comment #3 from hongleij at 126 dot com  2006-12-30 13:46 -------
the question is : if a const member function can call a non_const member
function
without const_cast,
if fun() changed the member in A,like this:
//const_test.cpp
struct A
{
  A(unsigned int n)
  {
     aa=n;        
  }
  void const_fun() const
  {
      static_cast<A>(*this).fun();  //ok
     // fun();       //err  
  }
  void fun()
  {
     aa=78;
  }
  unsigned int aa;
};

int main()
{
    const A a(56);
    a.const_fun();
}
the sematic of bitwise constness is not confirmed.
this program is inspired from the book <Effective C++>(third edition)
Item3: use const whenever possible


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30331

[Bug c++/30331] a const member function can call a non_const member function without const_cast

[hongleij at 126 dot com]

------- Comment #4 from hongleij at 126 dot com  2006-12-30 13:48 -------
(In reply to comment #3)
> the question is : if a const member function can call a non_const member
> function
> without const_cast,
> if fun() changed the member in A,like this:
> //const_test.cpp
> struct A
> {
>   A(unsigned int n)
>   {
>      aa=n;        
>   }
>   void const_fun() const
>   {
>       static_cast<A>(*this).fun();  //ok
>      // fun();       //err  
>   }
>   void fun()
>   {
>      aa=78;
>   }
>   unsigned int aa;
> };
> 
> int main()
> {
>     const A a(56);
>     a.const_fun();
> }
> the sematic of bitwise constness is not confirmed.
> this program is inspired from the book <Effective C++>(third edition)
> Item3: use const whenever possible
  i do hope the compiler at least give a worning!
> 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30331

[Bug c++/30331] a const member function can call a non_const member function without const_cast

[gdr at integrable-solutions dot net]

------- Comment #5 from gdr at integrable-solutions dot net  2006-12-30 17:51 -------
Subject: Re:  a const member function can call a non_const member function
without const_cast

"hongleij at 126 dot com" <gcc-bugzilla@gcc.gnu.org> writes:

| the question is : if a const member function can call a non_const member
| function
| without const_cast,

[...]

| this program is inspired from the book <Effective C++>(third edition)
| Item3: use const whenever possible

This question is better asked and answered on C++ newsgroup.

-- Gaby


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30331

[Bug c++/30331] a const member function can call a non_const member function without const_cast

[pinskia at gcc dot gnu dot org]

------- Comment #7 from pinskia at gcc dot gnu dot org  2006-12-30 17:53 -------
Invalid as explained by me and Gaby.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30331

[Bug c++/30331] a const member function can call a non_const member function without const_cast

[gdr at gcc dot gnu dot org]

------- Comment #6 from gdr at gcc dot gnu dot org  2006-12-30 17:52 -------
user mistaken.


-- 

gdr at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30331

[Bug c++/30331] a const member function can call a non_const member function without const_cast

[hongleij at 126 dot com]

------- Comment #8 from hongleij at 126 dot com  2006-12-31 02:24 -------
(In reply to comment #7)
> Invalid as explained by me and Gaby.
> 

yes,it's my misuse.
really sorry for my wrong report.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30331