How can I pass a class member function as a callback?

Question

I\'m using an API that requires me to pass a function pointer as a callback. I\'m trying to use this API from my class but I\'m getting compilation errors.

Here is

Answer 1

This answer is a reply to a comment above and does not work with VisualStudio 2008 but should be preferred with more recent compilers.

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Meanwhile you don't have to use a void pointer anymore and there is also no need for boost since std::bind and std::function are available. One advantage (in comparison to void pointers) is type safety since the return type and the arguments are explicitly stated using std::function:

// std::function
void Init(std::function f);

Then you can create the function pointer with std::bind and pass it to Init:

auto cLoggersInfraInstance = CLoggersInfra();
auto callback = std::bind(&CLoggersInfra::RedundencyManagerCallBack, cLoggersInfraInstance);
Init(callback);

Complete example for using std::bind with member, static members and non member functions:

#include 
#include 
#include 

class RedundencyManager // incl. Typo ;-)
{
public:
    // std::function
    std::string Init(std::function f) 
    {
        return f();
    }
};

class CLoggersInfra
{
private:
    std::string member = "Hello from non static member callback!";

public:
    static std::string RedundencyManagerCallBack()
    {
        return "Hello from static member callback!";
    }

    std::string NonStaticRedundencyManagerCallBack()
    {
        return member;
    }
};

std::string NonMemberCallBack()
{
    return "Hello from non member function!";
}

int main()
{
    auto instance = RedundencyManager();

    auto callback1 = std::bind(&NonMemberCallBack);
    std::cout << instance.Init(callback1) << "\n";

    // Similar to non member function.
    auto callback2 = std::bind(&CLoggersInfra::RedundencyManagerCallBack);
    std::cout << instance.Init(callback2) << "\n";

    // Class instance is passed to std::bind as second argument.
    // (heed that I call the constructor of CLoggersInfra)
    auto callback3 = std::bind(&CLoggersInfra::NonStaticRedundencyManagerCallBack,
                               CLoggersInfra()); 
    std::cout << instance.Init(callback3) << "\n";
}

Possible output:

Hello from non member function!
Hello from static member callback!
Hello from non static member callback!

Furthermore using std::placeholders you can dynamically pass arguments to the callback (e.g. this enables the usage of return f("MyString"); in Init if f has a string parameter).