指向成员函数的指针数组：使其工作

Question

In the following code I am getting the error:

a value of type (double*)(const double& arg) const cannot be assigned to an entity of type pt2calculateA

Any suggestions on how to make it work?

class myClass {
    private:

    typedef double (*pt2calculateA)(double);

    pt2calculateA calculateA[2];

public:

    myClass () {
        calculateA[0] = &calculateA1; //->error
        calculateA[1] = &calculateA2; //->error
    }

    double calculateA1(const double& arg) const {
            ...
    }

    double calculateA2(const double& arg) const {
        ...
    }
}

Answer 1

myClass::calculateA1() is not a function ; rather, it is a member function . So the types are naturally not compatible.

The type of &myClass::calculcateA1 is double (myClass::*)(const double &) const , which is a pointer-to-member-function (PTFM). Note that you can only use a PTMF together with a pointer to an object instance (ie a myClass* ).

If you change your typedef, you could at least store the pointers correctly:

typedef double (myClass::*pt2calculateA)(const double &) const;

You'll have to say &myClass::calculateA1 , etc., to take the address.

In C++11, you can initialize the array in the initializer list:

myClass() : calculateA{&myClass::calculateA1, &myClass::calculateA2} { }

Answer 2

Try this:

class myClass {
    private:

    typedef double (myClass::*pt2calculateA)(const double&) const;

    pt2calculateA calculateA[2];

public:

    myClass () {
        calculateA[0] = &myClass::calculateA1;
        calculateA[1] = &myClass::calculateA2;
    }

    double calculateA1(const double& arg) const {
        //    ...
    }

    double calculateA2(const double& arg) const {
        //  ...
    }
};

Answer 3

Not only the parameter type differs between the typedef and the actual functions, but also one is a function pointer while the other is a member function pointer. myClass::calculateA1 has type double (myClass::*)(const double& arg) const .

Answer 4

pt2calculateA is declared as a pointer-to-function, not a pointer-to-member-function.

see here