Function pointers

When an application is run, the functions it will call will exist in memory somewhere. This means that you can get the address of a function. C++ allows you to use the function call operator (a pair of parentheses enclosing the parameters ()) to call a function through a function pointer.

Remember the parentheses!

First, a simple example of how function pointers can cause difficult to notice bugs in your code. A global function called get_status performs various validation actions to determine if the state of the system is valid. The function returns a value of zero to mean that the system state is valid and values over zero are error codes:

    // values over zero are error codes 
    int get_status() 
    { 
        int status = 0;  
        // code that checks the state of data is valid 
        return status; 
    }

The code could be called like this:

    if (get_status > 0) 
    { 
        cout << "system state is invalid" << endl; 
    }

This is an error...