如何通过迭代器通过指针调用函数？

Question

I have declared a global type:

typedef void ( MyClass::*FunctionPtr ) ( std::string );

then I need to use it in my function:

void MyClass::testFunc() {
}
void MyClass::myFunction() {

    std::map < std::string, FunctionPtr > ptrsMap;
    ptrsMap[ "first" ] = &MyClass::testFunc;

    std::map < std::string, FunctionPtr >::iterator it;
    it = ptrsMap.begin();

    ( *it->second ) ( "param" );    // How to call this function?

}

Problem is to call function by pointer using iterator of std::map. How to call that function?

I suppose all will work fine if I declare "it" as a global variable and call smth like that:

( this->*it->second ) ( "param" );

but I need to call that function using a local variable.

Answer 1

FunctionPtr is a member function pointer, so it needs to be called on an object. Using the pointer-to-member binding operator .* :

MyClass object;
...
(object.*it->second)("param")

Answer 2

The member function needs to be associated with an instance.

    MyClass k;
    (k.*it->second)("param");

or you can use the current object

(*this.*it->second)("param");

Also your testFunc needs to take a string parameter.

Answer 3

The problem is that a member function needs an object to be applied on.

One way to do this is with function objects:

auto f = std::bind(it->second, this, std::placeholders::_1);  // first bind is for object
f (std::string("param"));    // How to call this function?

By the way, in your code sample, you should correct the signature of the test function to:

void MyClass::testFunc(std::string)  //  FunctionPtr requires a string argument