Question

I have a rather unusual problem… we are tasked with mapping a series of hexadecimal values to function pointers. However, I want to be able to call the function with already predefined parameters. Here is a segment of code that I am trying to get to work:

map<short, void(*)(MyClass, MyClass)> mapping = create_map();


map<short, void(*)(MyClass, MyClass)> create_map()
{
    map<short, void(*)(MyClass, MyClass)>> m;
    m[1] = &function(new MyClass(), new MyClass());
    return m;
}

However, it will only let me put function without parameters into the mapping. How do I store this setup and call it later?

Answer 1

If you are using C++11, You can use std::bind:

void function(MyClass* a, MyClass* b) { ... }

typedef map<short, std::function<void()>> funcmap;

funcmap create_map()
{
    funcmap m;
    m[1] = std::bind(function, new MyClass, new MyClass);
    return m;
}

// use:

funcmap mapping = create_map();
mapping[1]();

If not, you can create a struct that stores the arguments and the function pointer. Then write an operator() which will call the function through the function pointer with the arguments it stored:

struct func {
    typedef void(*fptr)(MyClass*, MyClass*);

    func(fptr f, MyClass* m1, MyClass* m2) : ptr(f), arg1(m1), arg2(m2) { }

    void operator()() {
        ptr(arg1, arg2);
    }

    T ptr;
    MyClass* arg1, arg2;
};

void function(MyClass* a, MyClass* b) { ... }

typedef map<short, func> funcmap;

funcmap create_map()
{
    funcmap m;
    m[1] = func(function, new MyClass, new MyClass);
    return m;
}

// use:

map<short, func> mapping = create_map();
mapping[1]();