list/vector of class methods in a class variable

Question

I need to maintain a list of methods that will be executed in different orders for testing. We are moving away from C to C++ to use google framework. Is it possible to maintain a list of functions pointers to some of the class methods to be used for execution inside the class, so that they can be used after instantiation ? please refer http://cpp.sh/265y

#include <iostream>
#include <string>
#include <vector>
using namespace std;

typedef void (*funcType)();

class Sample {
    public:
    vector<funcType> func_list;

    Sample();

    void formList();
    void method1();
    void method2();
    void method3();    
};

void Sample::formList() {
    func_list.push_back(&method1);
    func_list.push_back(&method2);
    func_list.push_back(&method3);
}

void Sample::method1 () {
    cout << "method1" << endl;
}

void Sample::method2 () {
    cout << "method2" << endl;
}

void Sample::method3 () {
    cout << "method3" << endl;
}

int main()
{
    Sample sample; //* = new Sample();
    sample.formList();
    vector<funcType>::iterator it;
    for (it = sample.func_list.begin(); it != sample.func_list.end(); ++it) {
         ((*it));
    }

}

Answer: http://cpp.sh/8rr2

Answer 1

Introduction

You have currently declared funcType as an alias for void(*)(), which is a pointer to some function that takes no argument and returns void. What you should be using is a pointer-to-member-function, since this will fit the entities which you are trying to invoke.

class Sample;
typedef void (Sample::*funcType)(); 

You will also have to qualify your member-functions when you are to take their address:

void Sample::formList() {
    func_list.push_back(&Sample::method1);
    func_list.push_back(&Sample::method2);
    func_list.push_back(&Sample::method3);
}

When invoking a member-function you will need an object on which you would like to call it, this means that you—in order to invoke a member-function throug ha pointer-to-member-function—must supply an object at the call site.

for (it = sample.func_list.begin(); it != sample.func_list.end(); ++it) {
     (sample.*(*it)) (); // invoke the member-function referred to by `it`
}                        // on the object named `sample`

---

Further Reading

• stackoverflow.com - Calling member-function pointer
• cppreference.com - Pointers to member functions

---

---

Sample Implementation

#include <iostream>
#include <string>
#include <vector>
using namespace std;

class Sample;
typedef void (Sample::*funcType)();

class Sample {
  public:
    vector<funcType> func_list;

    void formList();
    void method1();
    void method2();
    void method3();    
};

void Sample::formList() {
  func_list.push_back(&Sample::method1);
  func_list.push_back(&Sample::method2);
  func_list.push_back(&Sample::method3);
}

void Sample::method1 () {
  cout << "method1" << endl;
}

void Sample::method2 () {
  cout << "method2" << endl;
}

void Sample::method3 () {
  cout << "method3" << endl;
}

int main()
{
  Sample sample; //* = new Sample();
  sample.formList();
  vector<funcType>::iterator it;
  for (it = sample.func_list.begin(); it != sample.func_list.end(); ++it) {
    (sample.*(*it)) ();
  }
}

method1
method2
method3

Answer 2

You could use the dreaded pointer-to-member-function syntax:

Live On Coliru

// Example program
#include <iostream>
#include <string>
#include <vector>
using namespace std;

class Sample;

typedef void (Sample::*funcType)();

class Sample {
  public:
    vector<funcType> func_list;

    Sample(){}

    void formList();
    void method1();
    void method2();
    void method3();
};

void Sample::formList() {
    func_list.push_back(&Sample::method1);
    func_list.push_back(&Sample::method2);
    func_list.push_back(&Sample::method3);
}

void Sample::method1() { cout << "method1" << endl; }

void Sample::method2() { cout << "method2" << endl; }

void Sample::method3() { cout << "method3" << endl; }

int main() {
    Sample sample; //* = new Sample();
    sample.formList();
    vector<funcType>::iterator it;
    for (it = sample.func_list.begin(); it != sample.func_list.end(); ++it) {
        (sample.*(*it))(); // HORRIFIC, INNIT? SEE BELOW FOR BETTER
    }
}

MUCH BETTER:

However, you could be much more versatile using C++11/TR1 std::function<> or boost::function<>:

typedef function<void(Sample*)> funcType;

// ...
func_list.push_back(mem_fn(&Sample::method1));
func_list.push_back(mem_fn(&Sample::method2));
func_list.push_back(mem_fn(&Sample::method3));

See it Live On Coliru too

for (it = sample.func_list.begin(); it != sample.func_list.end(); ++it) {
    (*it)(&sample); // much better
}

The added versatility is mainly in that you can cater for different signatures: Live On Coliru

class Sample {
  public:
    vector<funcType> func_list;

    Sample(){}

    void formList();
    void method1(int);
    void method2(std::string);
    void method3(double, double, double);
};

void Sample::formList() {
    using std::placeholders::_1;
    func_list.push_back(bind(&Sample::method1, _1, 42));
    func_list.push_back(bind(&Sample::method2, _1, "Hello world"));
    func_list.push_back(bind(&Sample::method3, _1, 1, 2, 3));
}