Question

I’m attempting to pass a pointer to a function that is defined in one class into another class. After much research, I believe my syntax is correct, but I am still getting compiler errors. Here is some code which demonstrates my issue:

class Base { public:     BaseClass();     virtual ~BaseClass(); };  class Derived : public Base { public:     // assign strFunction to the function pointer passed in     Derived(string (*funPtr)(int)) : strFunction(funPtr);     ~Derived();  private:     // pointer to the function that is passed in     string (*strFunction)(int value); };  class MainClass { public:     MainClass()     {         // allocate a new Derived class and pass it a pointer to myFunction         Base* myClass = new Derived(&MainClass::myFunction);         }      string myFunction(int value)     {         // return a string     } }; 

When I try to compile this code, the error I get is

error: no matching function for call to ‘Derived::Derived(string (MainClass::*)(int))’

followed by

note: candidates are: Derived::Derived(string (*)(int))

Any idea what I might be doing wrong?

Answer 1

your syntax is correct for a C style function pointer. Change it to this:

Derived(string (MainClass::*funPtr)(int)) : strFunction(funPtr) {} 

and

string (MainClass::*strFunction)(int value); 

remember to call strFunction, you will need an instance of a MainClass object. Often I find it useful to use typedefs.

typedef string (MainClass::*func_t)(int); func_t strFunction; 

and

Derived(func_t funPtr) : strFunction(funPtr) {}