C++ function pointer class not compiling in GCC? - c++

Question

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;
}

Answer 1

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.

Answer 2

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?

Answer 3

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"; } );