Adcanced Function

Cpp Learning Notes 10

Keypoints

• Default arguments
• Placeholder parameters
• Function overloading

Default arguments

• Syntax: return type function_name(type1 arg1, type2 arg2 = default_value);
  • The default value would be overwritten if the argument is passed in the function call
  • The arguments with default values must be at the end of the argument list
    • int func(int a, int b = 10, int c); is not allowed
  • If the declaration and definition are separated, the default value must be specified in the declaration, cannot be in the definition
    • int func(int a, int b = 10, int c); in the declaration
    • int func(int a, int b, int c){...} in the definition
• Example:

    #include <iostream>
    using namespace std;
    int func(int a, int b = 10, int c = 20){
        return a + b + c;
    }
  
    int main(){
        cout << func(10) << endl; // 40
        cout << func(10, 30) << endl; // 60
        cout << func(10, 30, 40) << endl; // 80
        return 0;
    }
  

Placeholder parameters

• Syntax: return type function_name(type1 arg1, type2)
• Example:

    #include <iostream>
    using namespace std;
    int func(int a, int){
        return a;
    }
  
    int main(){
        cout << func(10, 20) << endl; // 10
        return 0;
    }
  

Function overloading

• Function name can be reused if:
  • In the same scope
  • Function name is the same
  • Function parameters are different in number, type, or sequence.
    • Return type is not considered
  • Example:

      #include <iostream>
      using namespace std;
    
      void func(){
          cout << "func()" << endl;
      }
    
      void func(int a){
          cout << "func(int a)" << endl;
      }
    
      void func(double a){
          cout << "func(double a)" << endl;
      }
    
      void func(int a, double b){
          cout << "func(int a, double b)" << endl;
      }
    
      void func(double a, int b){
          cout << "func(double a, int b)" << endl;
      }
    
      int main(){
          func(); // func()
          func(10);   // func(int a)
          func(3.14); // func(double a)
          func(10, 3.14); // func(int a, double b)
          func(3.14, 10); // func(double a, int b)
          return 0;
      }
    

• Reference parameters can be overloaded with value parameters
  • The compiler will always choose the value parameter
  • The compiler will always choose the const reference parameter
  • Example:

    #include <iostream>
    using namespace std;
    
    void func(int &a){
        cout << "func(int &a)" << endl;
    }
    
    void func(const int &a){
        cout << "func(const int &a)" << endl;
    }
    
    int main(){
        int a = 10;
        func(a); // func(int &a), essentially func(int &a = a)
        func(10); // func(const int &a), essentially func(const int &a = 10)
        return 0;
    }
    

• Function overloading and default arguments
  • Example

    #include <iostream>
    using namespace std;
    
    void func(int a, int b = 10){
        cout << "func(int a, int b = 10)" << endl;
    }
    
    void func(int a){
        cout << "func(int a)" << endl;
    }
    
    int main(){
        func(10); // Error: call of overloaded 'func(int)' is AMBUGUOUS!
        func(10, 20); // func(int a, int b = 10), no ambiguity here
        return 0;
    }
    

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