Modifying Algorithms

Lesson 21 of 23 in Coddy's C++ - Standard Template Library course.

In this lesson you will learn about modifying algorithms that are present in the C++ STL.
Modifying algorithms are designed to alter the value of the elements within a container.

We will be covering the following algorithms:

copy()
fill()
move()
swap()
reverse()

`copy()` method

The copy() method copies the elements from the range of two defined iterators into the range starting by the third iterator

vector<int> v1 = {1, 2, 3};
vector<int> v2;

copy(v1.begin(), v1.end(), v2.begin());

for(auto value : v1)
	cout << value << " ";

Output:
1 2 3

We used the copy() method to copy the content of the vector v1 to the vector v2.

`fill()` method

This method assigns every element in the given range defined by two iterators, with a given value.

vector<int> numbers(10); // creates an empty vector with 10 elements

fill(numbers.begin(), numbers.end(), 1);

for(auto value : numbers)
	cout << value << " ";

cout << endl;

fill(numbers.begin(), numbers.end() - 3, 2);

for(auto value : numbers)
	cout << value << " ";

Output:
1 1 1 1 1 1 1 1 1 1
2 2 2 2 2 2 2 1 1 1

`move()` method

This method moves the elements from the current container and returns its rvalue.

vector<string> names;

string first = "John";
string second = "Max";

names.push_back(first);
names.push_back(move(second));

cout << first << endl;
cout << second << endl;
cout << names[1];

Output:
John

Max

As you can see, the move() method, empties the string, but returns it's value and the push_back() method insert the value in the vector.

`swap()` method

This method swaps the elements of two containers of the same type.

vector<int> v1 = {1, 2, 3};
vector<int> v2 = {4, 5, 6};

for(auto value : v1)
	cout << value << " ";
for(auto value : v2)
	cout << value << " ";

cout << endl;

swap(v1, v2);

for(auto value : v1)
	cout << value << " ";
for(auto value : v2)
	cout << value << " ";

Output:
1 2 3 4 5 6
4 5 6 1 2 3

`reverse()` method

This method reverses the order of the elements of one container, more precisely in the range of the two iterators.

vector<int> a = {1, 2, 3, 4, 5};

for(auto value : a)
	cout << value << " ";
	
cout << endl;
	
reverse(a.begin(), a.end());

for(auto value : a)
	cout << value << " ";