Pointer-to-member Strange behaviour

Pointer-to-member Strange behaviour

[Benoit Lavigne]

The following code won't compile, and I can't figure out why...
class Test {
public:
  int fn0();

};

int Test::fn0() {
  return 0;
}

class mgr_Param {
protected:

  Test* d_mgr_p;  // Manager object pointer

public:
  mgr_Param(Test *mgr_p) : d_mgr_p(mgr_p) { }

  virtual int Execute() = 0;

};

// Convenient typedef
typedef int (Test::* ptm)();

class mgr_Param0 : public mgr_Param
{
protected:

  ptm fn; // pointer to member function

public:
  mgr_Param0(Test* m_p, ptm f) : mgr_Param(m_p), fn(f) { }

  int Execute() {
    return (d_mgr_p->*fn);
  }
};

mgr_Param* CreateParam(Test* mgr_p, ptm f)
{
  return(new mgr_Param0(mgr_p, f));
}

int main() {

  mgr_Param* t1;
  Test       test;
  t1 = CreateParam(&test, &Test::fn0);
  t1->Execute();
};

gcc-2.7.2.3 gives:
test1.cc: In method `int mgr_Param0::Execute()':
test1.cc:51: Internal compiler error 308.
test1.cc:51: Please submit a full bug report to 

egcs-1.0 (great work by the way!):
test1.cc: In method `int mgr_Param0::Execute()':
test1.cc:51: warning: assuming & on `(*mgr_Param::d_mgr_p) .*
mgr_Param0::fn'
test1.cc:51: sorry, not implemented: address of bound pointer-to-member
expression


What I want to do:
  Call a function on a class instance, with a given set of parameters.
  The original code is templatized to handle the arbitrary case:

   Class  instance;
   t1 = CreateParam(&instance, &Class::SomeFunc, FuncP1 p1, ...pn);
   t1->Execute() // does instance->SomeFunc(p1, ... pn);


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Re: Pointer-to-member Strange behaviour

[Alexandre Oliva]

Benoit Lavigne writes:

> The following code won't compile, and I can't figure out why...

>   ptm fn; // pointer to member function
>   int Execute() {
>     return (d_mgr_p->*fn);

If you intend to call invoke the member function, you must add parens:
      return (d_mgr_p->*fn());

-- 
Alexandre Oliva
mailto:oliva@dcc.unicamp.br mailto:aoliva@acm.org
http://www.dcc.unicamp.br/~oliva
Universidade Estadual de Campinas, SP, Brasil