I would like help with my basic callback function pointer library

[d0773d]

Hi all,
I am attempting to wrap my brain around function pointers. I created two files, exeCallback.h and exeCallback.cpp. I am receiving the error: "expression must have (pointer-to-) function type". The error resides at:

foo(2);

After reading that error, I edited the line that was giving me the error to

exeCallback->foo(2);

.

exeCallback->foo(2);

throws two new errors that are, expected an identifier and expected a type specifier. What am I not doing to get my basic callback library to work successfully?

exeCallback.h code:

/*
File: exeCallback.h

Header file for exeCommand Library.
*/

#ifndef EXECALLBACK_H
#define EXECALLBACK_H

#include "mbed.h"

#include <functional>

#include <map>

class exeCallback
{
public:
    exeCallback();
    
    void my_int_func(int x);
    
    void (exeCallback::*foo)(int);

private:
};

#endif

exeCallback.cpp file code:

/*
File: exeCallback.cpp

Execute functions in other Sensor libraries/classes

Constructor
*/

#include "mbed.h"
#include "ConfigFile.h"
#include "msExtensions.h"
#include "cfExtensions.h"
#include "exeCallback.h"

exeCallback::exeCallback()
{
    
    foo = &exeCallback::my_int_func;

    foo(2);

}

void exeCallback::my_int_func(int x)
{
    printf( "%d\n", x );
}

[grumpy]

You're not playing with pointers to functions. You're playing with pointers to members (it just so happens the member you're playing with is a member function). They are different things.

To use a pointer to member it is necessary to explicitly tell the compiler what object the member is for. So ... foo(2) needs to be

        (this->*foo)(2);

or

       (*this.*foo)(2);

[d0773d]

You're not playing with pointers to functions. You're playing with pointers to members (it just so happens the member you're playing with is a member function). They are different things.

To use a pointer to member it is necessary to explicitly tell the compiler what object the member is for. So ... foo(2) needs to be

        (this->*foo)(2);

or

       (*this.*foo)(2);

Thank you. Your explaination helped.

(this->*foo)(2);

worked successfully.