如何在模板 function 中执行 function 指针？

Question

I want a function that can be called inside of another class which has a single input parameter of type void function pointer. Inside the function, the function pointer should execute the function to which it's pointing.

// inside TestClass.h
class TestClass
{
public:
    template<class UserClass>
    static void TestingFctPtrStatic(void (UserClass::* TestFunction)(void));
};

template<class UserClass>
inline void TestClass::TestingFctPtrStatic(void(UserClass::* TestFunction)(void))
{
    TestFunction();
}

Calling the function like this gives me the following compile error:

TestClass::TestingFctPtrStatic<TestClass>(&TestClass::PrintStuff);

With PrintStuff():

void TestClass::PrintStuff()
{
    std::cout << "Printing stuff!" << std::endl;
}

: error C2064: term does not evaluate to a function taking 0 arguments: message: see reference to function template instantiation 'void TestClass::TestingFctPtrNonStatic(void (__cdecl TestClass::* )(void))' being compiled

Answer 1

void(UserClass::* TestFunction)(void)

This is not a pointer to a function. It is a pointer to a class method.

TestFunction();

You can't just call a class method out of thin air. You need an object, an instance of the class, whose method gets called. If p is a pointer to a UserClass , in other words:

UserClass *p=(points to somewhere);

then you would invoke its method using this syntax:

(p->*TestFunction)();

It is unclear from your question's description where the object whose method gets invoked comes from, so you need to figure it out, yourself, based on all the other information you have but was not included in the question. In some form or fashion you'll need to find a UserClass object, somewhere -- either passed in as an additional parameter, or it's lying around, somewhere, in the general vicinity -- and then you can use the TestFunction pointer to invoke this object's method.

This is fundamental to C++, provided that this is a class method. If this PrintStuff is a static class method, then this would be, indeed, a plain old function pointer:

void (*TestFunction)();

And it would get invoke, via a pointer, no differently than any other function.