Function pointers by example

[Martin]

Function pointers are a powerful feature of C++.

code:

#include <iostream> using namespace std; int do_it(int x, int y, int (*func)(int,int)) {   return func(x,y); } int add(int x, int y) {   return x + y; } int subt(int x, int y) {   return x - y; } int mult(int x, int y) {   return x * y; } int main() {   int a, b, c = 1;   while(c!=0)   {     cout << "Hello. Would you like to\n0)Quit\n1) Add\n2) Subtract or\n3) Multiply\ntoday?" << endl;     cin >> c;     cout << "Give me a and b please" << endl;     cin >> a >> b;     if(c==1)       cout << a << " + " << b << " = " << do_it(a,b,add);     if(c==2)       cout << a << " - " << b << " = " << do_it(a,b,subt);     if(c==3)       cout << a << " * " << b << " = " << do_it(a,b,mult);     cout << endl << endl;   }   cout << "Au revoir!" << endl;    return 0; }

[wtd]

Actually. function pointers are a feature of C. C++ has an even better way to do this. Templates, type inference, and function objects.

code:

#include <iostream> #include <functional> using namespace std; template <typename T, typename F> T do_it(T x, T y, F func) {   return func(x, y); } int main() {   int a, b, c = 1;     while (c != 0)   {     cout << "Hello. Would you like to"<< endl          << "0)Quit" << endl          << "1) Add" << endl          << "2) Subtract or" << endl          << "3) Multiply" << endl          << "today?" << endl;               cin >> c;         cout << "Give me a and b please" << endl;         cin >> a >> b;         switch (c)     {       case 1:         cout << a << " + " << b << " = " << do_it(a, b, plus<int>());         break;       case 2:         cout << a << " - " << b << " = " << do_it(a, b, minus<int>());         break;       case 3:         cout << a << " * " << b << " = " << do_it(a, b, multiplies<int>());         break;     }         cout << endl << endl;   }     cout << "Au revoir!" << endl;     return 0; }

[avok23]

i have been using c++ for a good while and still havent found a reason to use this.
i hear its usefull in ai.

[wtd]

Think about callbacks.

[Saad]

wtd @ Thu Jun 08, 2006 9:12 am wrote:

Actually. function pointers are a feature of C. C++ has an even better way to do this. Templates, type inference, and function objects.

I never knew about this. This way seems much better and easier then funtion pointers. Thanks!

[Narlayusin]

It is the information that should be told to everyone really.

[ThomasWown]

@Martin - 100% Agreed! This is useful because functions encapsulate behavior. For instance, every time you need a particular behavior such as drawing a line, instead of writing out a bunch of code, all you need to do is call the function.