operator() with different args in derived functor

[andreaspp]

Hello,

I am trying to build a class which has two operator()-methods with different argument lists:

#include <iostream>
 
class base
{
  public:
    virtual double operator()() const { return 1; }
};
 
class derived : public base
{
  public:
    virtual double operator()( double x ) { return x;}
};
 
int main( int argc, char* argv[] )
{
  derived func;
  std::cout << func() << std::endl;        
  std::cout << func( 5 ) << std::endl;
  return 0;
}
 

gcc 4.1.0 aborts compilation with "error: no match for call to ‘(derived) ()’". There is no problem if the operator()(double) definition and usage is absent.

What am I doing wrong ?

Thanks in advance for your help,
Andreas

[sicarie]

Hello,

I am trying to build a class which has two operator()-methods with different argument lists:

#include <iostream>
 
class base
{
  public:
    virtual double operator()() const { return 1; }
};
 
class derived : public base
{
  public:
    virtual double operator()( double x ) { return x;}
};
 
int main( int argc, char* argv[] )
{
  derived func;
  std::cout << func() << std::endl;        
  std::cout << func( 5 ) << std::endl;
  return 0;
}
 

gcc 4.1.0 aborts compilation with "error: no match for call to ‘(derived) ()’". There is no problem if the operator()(double) definition and usage is absent.

What am I doing wrong ?

Thanks in advance for your help,
Andreas

Your error message is saying "no match for call'. This means that what you are using to pass to the fuction (your function call) does not match the definitions you have created for it. If you look, you are passing '5'. This is an int, while a double will have a remainder. Try 5.0.

[uppili]

i think you just try to use function concept. you nay get through

[andreaspp]

Thank you for your replies. I solved my problem.

The problem I had was the call func(), not func(5), and it was actually not related to the "operator()" name as I expected first.

The new operator()(double) method in "class derived" hides the operator()() method of its base class. I can avoid this feature by adding

using base::operator();

in "class derived".

Bye,
Andreas

[uppili]

when you are dealing with class you have to use the function concept (full like c program)

all the best