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error impllies the method is static, but method isn't static

janac (27)
I'm getting this error:
error C2355: 'this': can only be referenced inside non-static member functions or non-static data member initializers

I looked it up, and everywhere says the same thing, that I can't use the this pointer as a parameter for a static function, because the function doesn't belong to any particular object, so it doesn't have a this pointer. I get that, but I'm pretty sure I'm calling a member function (in main):
comp_2->get_mediator().notify(this, "This is from component 2."); // line 6

I was testing to make sure my code is correct to give me the type of the object sending the notification at runtime. (see lines 1, 2 and 3)

I haven't declared anything static. I checked to make sure the method is within the brackets of the class. What am I missing?

If I run the code below without line 6, the output is:
1
2
 
class ComponentTwo says: This is from component 2.
class ComponentOne says: This is from component 1.


If I run line 6 (not 4 and 5), I get the error at the top of my question.

Lines 4 and 5 simply call a method that gets the mediator and calls notify, so why is there any difference? (see lines 1, 2 and 3)

Here's the code:
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// error C2355: 'this': can only be referenced  inside non-static member functions or 
// non-static data member initializers

#include <iostream>
#include <string>
#include <typeinfo>

class BaseComponent;
class BaseMediator
{
public:
    virtual void notify(BaseComponent* sent_by, std::string message) const = 0;
};

class BaseComponent
{
protected:
    BaseMediator* mediator_ = nullptr;
public:
    BaseComponent(BaseMediator* mediator = nullptr) : mediator_(mediator){}
    void set_mediator(BaseMediator* mediator) { mediator_ = mediator; }
    BaseMediator& get_mediator(){ return *mediator_; }
    virtual void test_runtime_typeid() = 0; // line 1
};

class ComponentOne : public BaseComponent
{
private:

public:
    void test_runtime_typeid()
    {
        mediator_->notify(this, "This is from component 1."); // line 2
    }

};

class ComponentTwo : public BaseComponent
{
private:

public:
    void test_runtime_typeid()
    {
        mediator_->notify(this, "This is from component 2."); // line 3
    }
};

class Mediator : public BaseMediator
{
private:
    ComponentOne* comp_1_ = nullptr;
    ComponentTwo* comp_2_ = nullptr;

public:
    void notify(BaseComponent* sent_by, std::string message) const override
    {
        std::cout << typeid(*sent_by).name() << " says: " << message << '\n';
    }
    Mediator(ComponentOne* comp_1, ComponentTwo* comp_2) : comp_1_(comp_1), comp_2_(comp_2)
    {
        comp_1->set_mediator(this);
        comp_2->set_mediator(this);
    }
};

int main()
{
    ComponentOne* comp_1 = new ComponentOne();
    ComponentTwo* comp_2 = new ComponentTwo();
    Mediator* med = new Mediator(comp_1, comp_2);
    comp_2->test_runtime_typeid(); // line 4
    comp_1->test_runtime_typeid(); // line 5
    //comp_2->get_mediator().notify(this, "This is from the comp_2."); // line 6 error
}
Last edited on
Ganado (6810)
main is not part of a class, so it doesn't have access to a 'this' pointer.
Last edited on
deleted account xyzzy (5768)
Well, I don't know if this is a real fix, or a hacky hack, but consider changing line 74 to:
comp_2->get_mediator().notify(comp_2, "This is from the comp_2.");
deleted account xyzzy (5768)
Heh, change the comp_2 in the notify function to comp_1 and witness the output.
janac (27)
@Ganado Alright, I'll remember that. Thanks for the quick reply.

So, 'this' refers to the class surrounding the function, where it's currently begin called.
I think I assumed 'this' meant the class the function belongs to.
Last edited on
seeplus (6591)
Within a class, this is a pointer to the instantiation of that class.
deleted account xyzzy (5768)
janac (27)
@George P It works, so I'll keep it in mind.

Changing the parameter to comp_1 makes it really clear.
Last edited on
deleted account xyzzy (5768)
@janac, I am pleased I was able to help. :)
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