Question

I’m using boost::function to enable the passing of a function to a Button constructor so it holds that function. Calling it whenever it is activated.

typedef boost::function< void() > Action;

In my TitleState I’ve constructed a Button like this.

  m_play( 
    ButtonAction, // This is where I pass a function to Button's Action argument
    sf::Vector2f( 500, 400 ), 
    sf::IntRect( 500, 400, 700, 500 ) 
  )

where ButtonAction is a static void function privately held in TitleState’s header, defined in the implementation file as simply outputting to the console via std::cout (just as a test for whether it is working).

In my code, if the mouse clicks a button in TitleState’s HandleEvents function, the program calls that button’s Activate function which looks like this.

void Button::Activate() const {
  m_action(); // m_action is the Action member that holds the ButtonAction I passed earlier
}

The problem is that, when the program tries to link I get this error….

unresolved external symbol "public: void __thiscall Button::Activate(void)" (?Activate@Button@@QAEXXZ) referenced in function "public: virtual void __thiscall TitleState::HandleEvents(void)" (?HandleEvents@TitleState@@UAEXXZ)

I’m not sure what the problem is besides that the linker can’t find the definition of the function. Everything is #included or declared properly. Any assistance is appreciated. Thanks.

P.S. When I used the BoostPro installer, I only installed the single-threaded stuff and none of the multi-threaded stuff. Could this be a reason why it isn’t working? I read that linker problems can occur when libraries are linking in different ways. If this could be an issue, I’ll add that I’m also using the SFML library.

Answer 1

Add the library option when you are linking your program:

g++:

g++ -L/your/library/path -lyour_library_name

vc++:

• using boost with vc++