• L value - Associated with non-temporary objects
• string str = "hello";
• str - L Value
• "Hello" - R Value, Temporary

string x= findMax(a);
string & y = x;
cout << y << endl;

• R values can be moved (we do not need the value)
• L values can be copied

// Refrence to an R Value
string && str2 = "Hello";

Parameter Passing

Call by Value

• Copies the value of the parameter being passed
• Called function can modify the parameter but not the initial

Pass by Reference

• Can modify the original value
• Faster because you dont need to make a copy

Pass by Reference

• Cannot modify the value
• Should be used for large values

Call by rvalue refrence

• Move rvalue instead of copy
• Normally more efficient

vector <string> v("hello", "world");
cout << randomItem(v) << endl;  // L Value
cout << randomItem({"Hello", "World"}) << endl; // R Value

Given File Example

#include <iostream>
#include <vector>
#include <string.h>

using namespace std;


double ave( const vector<int> & arr, int n, bool & errorFlag)
{

    int sum = 0;
	for( int i = 0; i < arr.size( ); ++i )
	  sum += arr[i];

	n = 100;
	errorFlag = true;
	return ((double)sum)/arr.size();
}


int main( )
{
  int nn = 5;
  bool err = false;
  
  vector<int> myArray {1, 2, 3, 4, 5};
  double average = 0.0;
  
  cout << "Before: average = " << average << ", nn = " << nn << ", err = " << err << endl;  

  average = ave(myArray, nn, err);

  cout << " After: average = " << average << ", nn = " << nn << ", err = " << err << endl;  

  return 0;
}

Return Passing

Return by Value

• makes a copy of a variable returned

Return by Reference

• Return a reference of the variable returned

Return by Const Reference

• Return the reference of the variable returned
• Return value cannot be modified by caller

Lifeline extended beyond function call for by const reference and reference.

---

Big Five in C++

• Five special functions provided in all c++ classes
  • Destructor constructor
  • Copy constructor
  • Move constructor
  • Copy assignment operator =
  • Move assignment operator =

A constructor is called whenever..

• An object goes out of scope
• Delete is called Invoked during
• Declaration
• Call by value, and return by value
• Not in Assignment operator

---

Problem with Defaults

• Usually dont work when data member is a pointer type
• If a class contains pointers as member variables and you want two copies of objects pointed at

Variable Scope

• If your program sometimes doesn't work. Then... You Have Bugs
• a local variable only exists within its scope

---

Templates

• Type independent patterns
• Allows for reusable code, and generic programming
• The template declaration indicates that Comparable is the template argument it can be replaced by any type to produce a real function.

// Return the maximum item in the array a
template<typename Comparable>
const Comparable& findMax(const vector<Comparable>& a){
	int maxIndex = 0;
	for(int i= 1; i < a.size(); i++){
		if(a[maxIndex] < a[i]){
			maxIndex = i;
		}
	}
	return a[maxIndex];
}

For Example

• If a user needs to use the same function to hold a string, as well as integers. A Code example can be seen above.
• Also covered in [[COP3330]] notes

Function Objects

• Objects whose primary purpose is to define a function
• Using operator overloading : operator ()

Memory Cell

• Can be used for any type object

#code #functions #pass-by-ref #assignment #l-value #r-value #defaults #memberFunctions #memberVariables #declaration #cpp