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2010-05-25T14:21:17Z

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==Pass by reference by using pointer==

<source lang="cpp">#include <iostream>

void swap(int *x, int *y);

int main()
{
int x = 5, y = 10;

std::cout << "Main. Before swap, x: " << x << " y: " << y << "\n";
swap(&x,&y);
std::cout << "Main. After swap, x: " << x << " y: " << y << "\n";
return 0;
}

void swap (int *px, int *py)
{
int temp;

std::cout << "Swap. Before swap, *px: " << *px << " *py: " << *py << "\n";

temp = *px;
*px = *py;
*py = temp;

std::cout << "Swap. After swap, *px: " << *px << " *py: " << *py << "\n";
}</source>
<pre class=codeResult>Main. Before swap, x: 5 y: 10
Swap. Before swap, *px: 5 *py: 10
Swap. After swap, *px: 10 *py: 5
Main. After swap, x: 10 y: 5</pre>

==Pass by reference using references==

<source lang="cpp">#include <iostream>

void swap(int &x, int &y);

int main()
{
int x = 5, y = 10;

std::cout << "Main. Before swap, x: " << x
<< " y: " << y << "\n";
swap(x,y);
std::cout << "Main. After swap, x: " << x
<< " y: " << y << "\n";
return 0;
}

void swap (int &rx, int &ry)
{
int temp;

std::cout << "Swap. Before swap, rx: " << rx
<< " ry: " << ry << "\n";

temp = rx;
rx = ry;
ry = temp;

std::cout << "Swap. After swap, rx: " << rx
<< " ry: " << ry << "\n";
}</source>
<pre class=codeResult>Main. Before swap, x: 5 y: 10
Swap. Before swap, rx: 5 ry: 10
Swap. After swap, rx: 10 ry: 5
Main. After swap, x: 10 y: 5</pre>

==Passing references to objects==

<source lang="cpp">#include <iostream>

class MyClass
{
public:
MyClass();
MyClass(MyClass&);
~MyClass();

int GetAge() const { return itsAge; }
void SetAge(int age) { itsAge = age; }

private:
int itsAge;
};

MyClass::MyClass()
{
std::cout << "Simple Cat Constructor...\n";
itsAge = 1;
}

MyClass::MyClass(MyClass&)
{
std::cout << "Simple Cat Copy Constructor...\n";
}

MyClass::~MyClass()
{
std::cout << "Simple Cat Destructor...\n";
}

const MyClass & f (const MyClass & obj);

int main()
{
MyClass myObject;
std::cout << "myObject is " << myObject.GetAge() << " years old\n";

int age = 5;
myObject.SetAge(age);
std::cout << "myObject is " << myObject.GetAge() << " years old\n";

std::cout << "Calling f...\n";
f(myObject);
std::cout << "myObject is " << myObject.GetAge() << " years old\n";
return 0;
}

const MyClass & f (const MyClass & obj)
{
std::cout << "Function Two. Returning...\n";
std::cout << "myObject is now " << obj.GetAge()<< " years old \n";
return obj;
}</source>
<pre class=codeResult>Simple Cat Constructor...
myObject is 1 years old
myObject is 5 years old
Calling f...
Function Two. Returning...
myObject is now 5 years old
myObject is 5 years old
Simple Cat Destructor...</pre>

==Returning multiple values from a function using references==

<source lang="cpp">#include <iostream>
void f(int, int&, int&);

int main()
{
int number = 2, squared, cubed;
f(number, squared, cubed);

std::cout << "number: " << number << "\n";
std::cout << "square: " << squared << "\n";
std::cout << "cubed: " << cubed << "\n";
return 0;
}

void f(int n, int &rSquared, int &rCubed)
{
rSquared = n*n;
rCubed = n*n*n;
}</source>
<pre class=codeResult>number: 2
square: 4
cubed: 8</pre>

==Use reference parameters to create the swap() function.==

<source lang="cpp">#include <iostream>
using namespace std;

void swap(int &x, int &y);

int main()
{
int i, j;

i = 10;
j = 20;

cout << "Initial values of i and j: ";
cout << i << " " << j << "\n";

swap(j, i);

cout << "Swapped values of i and j: ";
cout << i << " " << j << "\n";

return 0;
}

void swap(int &x, int &y)
{
int temp;

temp = x;
x = y;
y = temp;
}</source>
<pre class=codeResult>Initial values of i and j: 10 20
Swapped values of i and j: 20 10</pre>

==Using a reference parameter.==

<source lang="cpp">#include <iostream>
using namespace std;

void f(int &i); // i is a reference parameter

int main()
{
int val = 1;

cout << "Old value for val: " << val << "\n";

f(val);

cout << "New value for val: " << val << "\n";

return 0;
}

void f(int &i)
{
i = 10;
}</source>
<pre class=codeResult>Old value for val: 1
New value for val: 10</pre>

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