Question

I have one application in which following task are to be done

1.) UI application will send command code (integer value).
2.) DLL interface(in c++) will get that integer value and execute corresponding command function.

commands name and command code are maintained as

#define PING 50

there will be 500 commands and applying SWITCH CASE will not sound good. so i decided to implement function pointer in my code as below

   #include "stdafx.h"

    #include<iostream>
    #define PING 20

    using namespace std;
    //extern const int PING = 10; 
    void ping()
    { 
                    cout<<"ping command executed";
    }


    void get_status(void)
    {


    cout<<"Get_status called"<<endl;

    }

    class ToDoCommands
    {
            public:
                void getCommand( void (*CommandToCall)() );                         
    };



    void ToDoCommands::getCommand( void (*CommandToCall)())
    {


        void (*CommandToCall1)();

        CommandToCall1  = CommandToCall;

        CommandToCall1();

    }

    int main()
    {
            int code;
            ToDoCommands obj;
            cout<<"enter command code";
            cin>>code;  // if UI send 50 then Ping function get executed as #define PING 50

            obj.getCommand(ping);   // here m passing ping manually..
            //obj.getCommand(get_status);

                return 0;
    }

how can i pass command name corresponding to command code in

obj.getCommand(ping); 

Answer 1

You are almost there: make a std::map of std::string to function pointer, initialize it with data pairing a string name to a corresponding function pointer, and then use that map at runtime to pick the correct pointer based on the string parameter passed in.

#include <iostream>
#include <string>
#include <map>

using namespace std;

void ping() {
    cout << "ping" << endl;
}
void test() {
    cout << "test" << endl;
}
int main() {
    map<string,void(*)()> m;
    m["ping"] = ping;
    m["test"] = test;
    // I am using hard-coded constants below.
    // In your case, strings will come from command line args
    m["test"]();
    m["ping"]();
    return 0;
}

Link to a demo with std::map.

Here is how you can do it without a map (it will be slower because of the linear search, but you can fix it by ordering names alphabetically and using binary search).

#include <iostream>
#include <cstring>

using namespace std;

void ping() {
    cout << "ping" << endl;
}
void test() {
    cout << "test" << endl;
}
typedef void (*fptr_t)();
int main() {
    const fptr_t fptrs[] = {test, ping};
    const char *names[] = {"test", "ping"};
    const char *fname = "test";
    for (int i = 0 ; i != 2 ; i++) {
        if (!strcmp(fname, names[i])) {
            fptrs[i]();
            break;
        }
    }
    return 0;
}

Link to a demo with arrays.