I have array of pointers of methods my class, but I cannot call my method. Code are below

Question

#include <iostream>
#include <stdio.h>
#include <stdint.h>
/* run this program using the console pauser or add your own getch, system("pause") or input loop */

 
class FooBar{
public:
        typedef void(FooBar::*OnDio)(void);

    void OnDio0Irq( void ){
        printf("dio0\n");
    };
    void OnDio1Irq( void ){
        printf("dio1\n");
    };
    FooBar(){
        OnDio  dioArray[] = {&OnDio0Irq, &OnDio1Irq};
        
    };
    
    OnDio  *dioArray[2];
private:
            
};
 
int main(int argc, char* argv[]){
        typedef void(FooBar::*OnDio)(void);
        void (FooBar::*foo)(void);
    OnDio *myPtr;
    FooBar *fb = new FooBar();
    
    myPtr = *(&fb->dioArray[0]);
    foo = (OnDio &)(myPtr[0]);
    (foo)();//me need call fb->dioArray[0]()
    (*myPtr)(); // ?
 }

How can I call a function from an array? In my code i have error:

[Error] must use '.' or '->' to call pointer-to-member function in 'foo (...)', e.g. '(... ->* foo) (...)'

[Error] must use '.' or '->' to call pointer-to-member function in '* myPtr (...)', e.g. '(... ->* * myPtr) (...)'

Look up the section titled Pointers to member functions at en.cppreference.com/w/cpp/language/pointer. — R Sahu
– R Sahu, Commented Nov 14, 2017 at 6:22

Kenny Ostrom · Accepted Answer · 2017-11-14 06:40:17Z

To call a pointer to member function (ptmf), you need an instance and the ptmf, together.

OnDio is already typedef'ed to be a pointer type, so you may not want OnDio pointers.

Also, you initialize a local temporary in the constructor, not the dioArray of "this" instance.

This answer is also helpful: C++: Array of member function pointers to different functions

Here is your code, corrected to call dio0 through a pointer to member function.

#include <iostream>
#include <stdio.h>
#include <stdint.h>

class FooBar {
public:
    typedef void(FooBar::*OnDio)(void);

    void OnDio0Irq(void) {
        printf("dio0\n");
    };
    void OnDio1Irq(void) {
        printf("dio1\n");
    };
    FooBar() {
        // declaring a local OnDio array just masks the actual member and then it gets tossed
        // need to initialize this instance, not some local temporary
        dioArray[0] = &FooBar::OnDio0Irq;
        dioArray[1] = &FooBar::OnDio1Irq;
    };

    OnDio dioArray[2];
private:

};

int main(int argc, char* argv[]) {
    // need instance
    FooBar fb;
    // need pointer to member function
    FooBar::OnDio func = fb.dioArray[0];
    // call pointer to member function using instance
    (fb.*func)();
}

Elad Hazan · Accepted Answer · 2017-11-14 07:06:36Z

0

#include <iostream>
#include <stdio.h>
#include <stdint.h>



class FooBar {
public:
    typedef void(FooBar::*OnDio)(void);
    OnDio dioArray[2];
    void OnDio0Irq(void) {
        printf("dio0\n");
    };
    void OnDio1Irq(void) {
        printf("dio1\n");
    };
    FooBar() {
        dioArray[0] = &FooBar::OnDio0Irq;
        dioArray[1] = &FooBar::OnDio1Irq;
    };


private:

};

int main(int argc, char* argv[]) {

    FooBar* fb  = new FooBar();
    for (int i = 0; i < sizeof(fb->dioArray) / sizeof(fb->dioArray[0]); i++)
    {
        (fb->*fb->dioArray[i])();
    }

}

answered Nov 14, 2017 at 7:06

Elad Hazan

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