I have already searched a lot, but cannot figure out the the correct syntax. All I'm trying results in some syntax errors. Without a member function I can get it to compile.

Here is my sample:

class TestClass
{
public:
  typedef bool (TestClass::* demoFunc)(int);
  struct Container
  {
    Container(demoFunc func)
        : func(func)
    {}
    demoFunc func;
  };

  Container* containers;

  bool foo1(int dummy) { return true; }
  bool foo2(int dummy) { return true; }

  void InvokeFunction(int i)
  {
    TestClass::Container container = containers[i];
    // How do I call the function here?
    bool result = container.func(0); // here is the error
  }
};

int main()
{
  TestClass testClass;
  testClass.containers = new TestClass::Container[]
  {
    TestClass::Container(&TestClass::foo1),
    TestClass::Container(&TestClass::foo2),
  };

  testClass.InvokeFunction(0);
  testClass.InvokeFunction(1);
}

This is the compler error:

expression preceding parentheses of apparent call must have (pointer-to-) function type

CodePudding user response：

The operator ->* allow you to call a member function using a pointer to the instance. The operator .* allow you to call a member function using directly an instance or a reference to an instance.

You can use them followed by your member function address in order to make a call to that function.

e.g.

struct Test
{
    bool foo(int val){ return true; }
};

int main()
{
    Test test_instance;
    Test* test_pointer = &test_instance;
    Test& test_reference = test_instance;
    
    auto FuncAddress = &Test::foo;
    
    //calling foo using pointer
    (test_pointer->*FuncAddress)(0);
    
    //calling foo using directly the instance
    (test_instance.*FuncAddress)(0);
    
    //calling foo using a reference to the instance
    (test_reference.*FuncAddress)(0);
    
    return 0;
}

CodePudding user response：

Dereferencing/calling a pointer-to-member requires a target object (of type TestClass, in this case).

Presumably you want to use this: bool result = (this->*container.func)(0);

CodePudding user response：

Pointers_to_members syntax is not trivial, in your case, it would be:

bool result = (this->*(container.func))(0);

As alternative, std::invoke (C 17) might be used

std::invoke(container.func, this, 0);