customer demand

• Write a function

  • Function to get the value of each term of Fibonacci series
  • Return one value per call
  • Functions can be reused as needed

Programming experiment: the first solution

#include <iostream>

using namespace std;

int fib()
{
    static int a0 = 0;
    static int a1 = 1;
    
    int ret = a1;
    
    a1 = a0 + a1;
    a0 = ret;
    
    return ret;
}

int main()
{
    for(int i=0; i<10; i++)
    {
        cout << fib() << endl;
    }
    
    cout << endl;
    
    for(int i=0; i<5; i++)
    {
        cout << fib() << endl;
    }
    
    return 0;
}

Output:
1
1
2
3
5
8
13
21
34
55

89
144
233
377
610

Existing problems

• Once a function is called, it cannot be called again

  • Static local variable is inside the function and cannot be changed outside
  • Function is a global function. It is unique and cannot be used independently multiple times
  • Cannot specify a specific sequence term as the initial value

Solution

• Function object

  • Replacing functions with concrete class objects
  • Objects of this class have the behavior of function calls
  • Constructor to specify the starting position of image items in a specific sequence
  • Solving sequence terms independently for multiple objects

Function object

• function call operator

  • Can only be overloaded by a class's member function
  • Multiple overloaded functions with different parameters can be defined

Programming experiment: the final solution

#include <iostream>

using namespace std;

class Fib
{
private:
    int a0;
    int a1;
public:
    Fib()
    {
        a0 = 0;
        a1 = 1;
    }
    
    Fib(int n)
    {
        a0 = 0;
        a1 = 1;
        
        for(int i=2; i<=n; i++)
        {
                int t = a1;
    
                a1 = a0 + a1;
                a0 = t;
        }
    }
    
    int operator () ()
    {
        int ret = a1;
    
        a1 = a0 + a1;
        a0 = ret;
    
        return ret;
    }
};

int main()
{
    Fib fib;

    for(int i=0; i<10; i++)
    {
        cout << fib() << endl;
    }
    
    cout << endl;
    
    for(int i=0; i<5; i++)
    {
        cout << fib() << endl;
    }
    
    cout << endl;
    
    Fib fib2(10);
    
    for(int i=0; i<5; i++)
    {
        cout << fib2() << endl;
    }
    
    return 0;
}

Output:
1
1
2
3
5
8
13
21
34
55

89
144
233
377
610

55
89
144
233
377

Summary

• Function call operator (()) is overloadable
• Function call operators can only be overloaded by class member functions
• Function call operators can define multiple overloaded functions with different parameters
• Function object is used to replace function pointer in Engineering

The above contents refer to the series courses of Ditai Software Institute, please protect the original!