CODEWITHSUNDEEP
c++c++11
Corbie
Corbie

Reputation: 1066

C++ Binding non-static member function

I am trying to pass a member function to another function in a nested class.

Passing a non-member function works well but passing the member does not compile:

A.h: 
class A
{
    class B
    {
        B();
        ~B();
        doSomething();
    };

    class C
    {
        C();
        ~C();
        execute(function<void(void)> func);
    };

    C *myC;
    map<int, B> myMap;
}
A.cpp: 
void A::member(int param)
{
    A::myMap[param].doSomething();
}

void nonA_func(int param)
{
    ...
}

void A::caller()
{
    myC->execute(bind(nonA_func, 42)); // OK
    myC->execute(bind(A::member, 42)); // COMPILER ERROR 1

    myC->execute(A::myMap[42].doSomething()); // COMPILER ERROR 2
}

A::main()
{
    myC = new A::C();
    // filling myMap

    caller();

    myMap.clear();
    delete C;
}

When compiling the following COMPILER ERROR 1 occurs:

error: invalid use of non-static member function  
    myC->execute(bind(A::member, 42));
                               ^

Actually defining A::member as static solves this problem, but then I can't access myMap anymore. How can I bind the non-static member function?

I have also tried to pass the called function directly, resulting in COMPILER ERROR 2:

 invalid use of void expression  
     myC->execute(A::myMap[42].doSomething());
                                       ^

Upvotes: 3

Views: 6339

Answers (1)

krzaq
krzaq

Reputation: 16421

You need to pass the this pointer to bind (or lambda). You can't use instance variables/functions without an instance.

myC->execute(bind(&A::member, this, 42));
myC->execute([this]{ member(42); });

Upvotes: 9

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