bound pointer to member

bound pointer to member

[Klaus Rudolph]

Hi,

I search for a simple code snipped which shows how bound pointers work.
I always end up in the message : 

main.cpp:51: error: ISO C++ forbids taking the address of a bound member function to form a pointer to member function.  Say ‘&A::Func2’

Can anyone post a code snippet which compiles on g++? Is there a need to give any special options to enable this language extension?

Thanks
 Klaus


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Re: bound pointer to member

[Jonathan Wakely]

On 23 February 2011 10:19, Klaus Rudolph wrote:
> Hi,
>
> I search for a simple code snipped which shows how bound pointers work.
> I always end up in the message :
>
> main.cpp:51: error: ISO C++ forbids taking the address of a bound member function to form a pointer to member function.  Say ‘&A::Func2’
>
> Can anyone post a code snippet which compiles on g++?

$ cat bound.cc
struct Sq {
  int f(int i) { return i*i; }
};

int main()
{
  typedef int (*funcptr_type)(Sq*, int);

  funcptr_type f = (funcptr_type)(&Sq::f);

  Sq sq;

  return f(&sq, 4);
}
$ g++ bound.cc -Wno-pmf-conversions
$ ./a.out ; echo $?
16
$


>Is there a need to give any special options to enable this language extension?

As stated in the manual, use -Wno-pmf-conversions to suppress a
warning, but it still works even if the warning is issued.

http://gcc.gnu.org/onlinedocs/gcc/Bound-member-functions.html

Re: bound pointer to member

[Klaus Rudolph]

> > Hi,
> >
> > I search for a simple code snipped which shows how bound pointers work.
> > I always end up in the message :
> >
> > main.cpp:51: error: ISO C++ forbids taking the address of a bound member
> function to form a pointer to member function.  Say ‘&A::Func2’
> >
> > Can anyone post a code snippet which compiles on g++?
> 
> $ cat bound.cc
> struct Sq {
>   int f(int i) { return i*i; }
> };
> 
> int main()
> {
>   typedef int (*funcptr_type)(Sq*, int);
> 
>   funcptr_type f = (funcptr_type)(&Sq::f);
> 
>   Sq sq;
> 
>   return f(&sq, 4);
> }

OK, maybe a missunderstanding or a wrong naming for my problem...

What I am searching for is the following:

class A 
{
    void AnyFunc();
}

int main()
{
   A a1;
   A a2;

   ...anyPointerDefinition ptr1;
   ...anyPointerDefinition ptr2;

   ptr1= &(a1.Func);
   ptr2= &(a2.Func);

   //call the pointers as functions
   ptr1();
   ptr2();   
}

where ptr1 and ptr2 must contain the ptr to the method and the ptr to
the object. This extension is available on borland as I know?!

Any idea?

Thanks
 Klaus
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Re: bound pointer to member

[Jonathan Wakely]

On 23 February 2011 10:54, Klaus Rudolph wrote:
>
> What I am searching for is the following:
>
> class A
> {
>    void AnyFunc();
> }
>
> int main()
> {
>   A a1;
>   A a2;
>
>   ...anyPointerDefinition ptr1;
>   ...anyPointerDefinition ptr2;
>
>   ptr1= &(a1.Func);
>   ptr2= &(a2.Func);
>
>   //call the pointers as functions
>   ptr1();
>   ptr2();
> }
>
> where ptr1 and ptr2 must contain the ptr to the method and the ptr to
> the object. This extension is available on borland as I know?!
>
> Any idea?

I don't think G++ supports that.

You can do it using the TR1 library extensions:

#include <tr1/functional>

struct A
{
    int f();
};

int main()
{
  using std::tr1::function;
  using std::tr1::bind;
  A a;
  function<int()> f = bind(&A::f, a);
  return f();
}

The same functionality is available in the Boost library too.

Re: bound pointer to member

[David Hagood]

On Wed, 2011-02-23 at 11:54 +0100, Klaus Rudolph wrote:
> OK, maybe a missunderstanding or a wrong naming for my problem...
> 
> What I am searching for is the following:
> 
> class A 
> {
>     void AnyFunc();
> }
> 
> int main()
> {
>    A a1;
>    A a2;
> 
>    ...anyPointerDefinition ptr1;
>    ...anyPointerDefinition ptr2;
> 
>    ptr1= &(a1.Func);
>    ptr2= &(a2.Func);
> 
>    //call the pointers as functions
>    ptr1();
>    ptr2();   
> }

You probably want to use the Boost Function library for this:
http://www.boost.org/doc/libs/1_46_0/doc/html/function/tutorial.html#id1275012