Software Best Practices

Hi all,

 I found in a tutorial on function pointers that apart from being used for Callback functions, the function pointers can also be used to replace switch statments. Please find below the example code for the same :

//------------------------------------------------------------------------------------
// 1.2 Introductory Example or How to Replace a Switch-Statement
// Task: Perform one of the four basic arithmetic operations specified by the
//       characters '+', '-', '*' or '/'.


// The four arithmetic operations ... one of these functions is selected
// at runtime with a swicth or a function pointer
float Plus    (float a, float b) { return a+b; }
float Minus   (float a, float b) { return a-b; }
float Multiply(float a, float b) { return a*b; }
float Divide  (float a, float b) { return a/b; }


// Solution with a switch-statement - <opCode> specifies which operation to execute
void Switch(float a, float b, char opCode)
{
   float result;

   // execute operation
   switch(opCode)
   {
      case '+' : result = Plus     (a, b); break;
      case '-' : result = Minus    (a, b); break;
      case '*' : result = Multiply (a, b); break;
      case '/' : result = Divide   (a, b); break;
   }

   cout << "Switch: 2+5=" << result << endl;         // display result
}


// Solution with a function pointer - <pt2Func> is a function pointer and points to
// a function which takes two floats and returns a float. The function pointer
// "specifies" which operation shall be executed.
void Switch_With_Function_Pointer(float a, float b, float (*pt2Func)(float, float))
{
   float result = pt2Func(a, b);    // call using function pointer

   cout << "Switch replaced by function pointer: 2-5=";  // display result
   cout << result << endl;
}


// Execute example code
void Replace_A_Switch()
{
   cout << endl << "Executing function 'Replace_A_Switch'" << endl;

   Switch(2, 5, /* '+' specifies function 'Plus' to be executed */ '+');
   Switch_With_Function_Pointer(2, 5, /* pointer to function 'Minus' */ &Minus);
}

I dont find any use of function pointers or even the need for switch statments here. A direct call to the function plus could be made 

in the function Replace_A_Switch instead of calling Switch. Hence, i could not appreciate the use of function pointers

in this context. Can anyone explain me better the use of function pointers other than for call back functions ?

Hoping to get a positive resoponse.

Thanks & Regards,

Ani 

I've used them a lot in older C code, but only for callbacks. For a better example, check out the documentation for the C QSort function. A famous place that they're used is the wondows 'WndProc' function that us still used internally in all windows libraries. http://www.toymaker.info/Games/html/wndproc.html

I'm more likely to use 'functors' or inheritance and virtual methods in C++ or delegates in C#.

Ralph