Array of function pointers to member functions

Question

I have the following code

#include<iostream>
using namespace std;
class operate
{
    int x;
    int y;
public:
    operate(int _x, int _y):x(_x), y(_y)
    {}
    void add(const char* ch)
    {
        cout<<ch<<" "<<x+y;
    }
    void subtract(const char* ch)
    {
        cout<<ch<<" "<<x-y;
    }
    void multiply(const char* ch)
    {
        cout<<ch<<" "<<x*y;
    }
};
int main()
{
    void (operate::*fptr[3])(const char*);
    operate obj(2,3);
    fptr[0] = &(operate.add);              //problem
    fptr[1] = &(operate.multiply);         //problem
    fptr[2] = &(operate.subtract);         //problem
    (obj.*fptr[0])("adding");
    (obj.*fptr[1])("multiplying");
    (obj.*fptr[2])("subtracting");
}

It seems I am not assigning the member functions to function pointer array properly. How can I solve this. I'm using VS2010

Please decide whether there is a mistake or not before posting a question. If you decided there is a mistake, tell us what behaviour you expect and what behaviour actually occurred. — Oswald
– Oswald, Commented Jul 16, 2013 at 8:41
@Oswald There is a mistake and VS2010 compiler isn't showing proper error message. It shows where to put punctuations and upon including those, again it is a compiler error — Saksham
– Saksham, Commented Jul 16, 2013 at 8:44

user529758 · Accepted Answer · 2013-07-16 08:44:45Z

4

The dot (member-of) operator is used for accessing members of an object. For classes and namespaces, you have to use the :: operator. Also, don't parenthesize, since & has lower precedence than :: and it's more readable like

fptr[0] = &operate::add;

answered Jul 16, 2013 at 8:44

user529758

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2 Comments

user1814023 Over a year ago

@H2CO3: Hi bro, want to have chat with you. Is it possible?

user529758 Over a year ago

@NishithJainMR Hi. Here you are.

ogni42 · Accepted Answer · 2013-07-16 09:04:40Z

0

This should do the job

void testFP()
{
    typedef void (operate::*memFP)(const char*); 
    memFP fptr[3];

    fptr[0] = &operate::add;
    fptr[1] = &operate::multiply;
    fptr[2] = &operate::subtract;
    operate op(42, 42);

    (op.*(fptr[0]))("adding");
}

answered Jul 16, 2013 at 9:04

ogni42

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