CODEWITHSUNDEEP
c++functionpointers
Cuthbert
Cuthbert

Reputation: 2998

C++ function pointer class not compiling in GCC?

I'm trying to make a class that can hold and later call functions. It stores the functions in a map along with a string that holds the name of the function.

I tried doing this on Linux with GCC and got the following error: "invalid conversion from void(*)() to void *" on the line functionsMap[nameOfFunction] = func;

Here's the entire program I have so far. It's not done yet, but I'm really curious as to why this would compile under Visual C++ and not GCC. If I'm doing something wrong or could be doing something better, please let me know. Thanks! 

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

class Dyn_Class{
private: 
    map<string, void *> functionsMap; 

public: 
    Dyn_Class(){} 

    template<typename ReturnValue>
    void add_func( string nameOfFunction, ReturnValue(*func)() ){
        functionsMap[nameOfFunction] = func; 
    }

    void remove_func( string nameOfFunction ){

    }

    Dyn_Class operator()(string nameOfFunction){

    }
}; 

void print(void){
    for(int index = 0; index < 9; index++){
        cout << index << "   "; 
    }
    cout << endl; 
}

int main(){
    Dyn_Class functionsList; 

    functionsList.add_func("print", print); 

    return 0; 
}

Upvotes: 1

Views: 309

Answers (3)

oopscene
oopscene

Reputation: 33

Think on using std::function instead:

class Dyn_Class{
private: 
    map<string, function<void()> > functionsMap; 

public: 
    Dyn_Class(){} 

    template<typename FUNC>
    void add_func(const string& nameOfFunction, FUNC func){
        functionsMap.insert(make_pair(nameOfFunction, func));
    }

    void remove_func(const string& nameOfFunction ){

    }

    void operator()(const string& nameOfFunction){
        functionsMap[nameOfFunction]();
    }
};

Benefits? Using "function", you could use your plain old function pointers, you can use functors or you can use lambda expressions instead:

DynClass dyn;
dyn.add("print", []() { printf("Say hi"; } );

Upvotes: 0

teo236
teo236

Reputation: 11

You can pass that function as a parameter like this:

void add(void * f()){...}

How do you pass a function as a parameter in C?

Upvotes: 0

CB Bailey
CB Bailey

Reputation: 792777

To have a map of pointers to function taking no arguments and returning void you need:

std::map<std::string, void(*)()> functionsMap;

There is no point making add_func a template as it will only work when instantiated with ReturnValue = void (unless you add a potentially unsafe cast to its implementation).

If your code compiles with Visual C++ it is because Visual C++ is being permissive.

Upvotes: 2

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