Question

We have a problem using a class template which itself uses function objects in some of its member functions. The error message form the VS2010 compiler is:

error C2512: ‘SimpleFunctor::SimpleFunctor’ : no appropriate default
constructor available

The downsized code to reproduce this is as follows:

// myfunctor.h

class SimpleFunctor
{
  private:
    SimpleFunctor( const SimpleFunctor& );
    SimpleFunctor& operator=( const SimpleFunctor& );
  public:
    bool operator()() { return true; }
}; 

// mytemplate.h

#include "myfunctor.h"

template< typename T >
class Test
{
  private:
    Test( const Test& );
    Test& operator=( const Test& );
  public:
    Test(){}

    void testFunction( T parameter )
    {
      bool result = SimpleFunctor()();
    }
};

// main.cpp

#include "HK_Template.h"

int main()
{
  Test< int > obj;
  obj.testFunction( 5 );

  return 0;
}

This examples produces the above error message which seems to be correct since adding the default constructor to class SimpleFunctor like:

SimpleFunctor() {}

fixes the error.

So the question is, why does the compiler not generate the default constructor?

Answer 1

Once you define any constructor yourself, including a copy constructor, the compiler doesn’t generate a default constructor anymore.

(On the other hand, a copy/move constructor is generated by default if you don’t provide one, subject to certain rules.)