Vector Functions

Iterators

1. begin() – Returns an iterator pointing to the first element in the vector

2. end() – Returns an iterator pointing to the theoretical element that follows the last element in the vector

3. rbegin() – Returns a reverse iterator pointing to the last element in the vector (reverse beginning). It moves from last to first element

4. rend() – Returns a reverse iterator pointing to the theoretical element preceding the first element in the vector (considered as reverse end)

5. cbegin() – Returns a constant iterator pointing to the first element in the vector.

6. cend() – Returns a constant iterator pointing to the theoretical element that follows the last element in the vector.

7. crbegin() – Returns a constant reverse iterator pointing to the last element in the vector (reverse beginning). It moves from last to first element

8. crend() – Returns a constant reverse iterator pointing to the theoretical element preceding the first element in the vector (considered as reverse end)

// C++ program to illustrate the 
// iterators in vector 
#include <iostream> 
#include <vector> 

using namespace std; 

int main() 
{ 
	vector<int> g1; 

	for (int i = 1; i <= 5; i++) 
		g1.push_back(i); 

	cout << "Output of begin and end: "; 
	for (auto i = g1.begin(); i != g1.end(); ++i) 
		cout << *i << " "; 

	cout << "\nOutput of cbegin and cend: "; 
	for (auto i = g1.cbegin(); i != g1.cend(); ++i) 
		cout << *i << " "; 

	cout << "\nOutput of rbegin and rend: "; 
	for (auto ir = g1.rbegin(); ir != g1.rend(); ++ir) 
		cout << *ir << " "; 

	cout << "\nOutput of crbegin and crend : "; 
	for (auto ir = g1.crbegin(); ir != g1.crend(); ++ir) 
		cout << *ir << " "; 

	return 0; 
} 

Output:

Output of begin and end: 1 2 3 4 5 
Output of cbegin and cend: 1 2 3 4 5 
Output of rbegin and rend: 5 4 3 2 1 
Output of crbegin and crend : 5 4 3 2 1

Capacity

1. size() – Returns the number of elements in the vector.

2. max_size() – Returns the maximum number of elements that the vector can hold.

3. capacity() – Returns the size of the storage space currently allocated to the vector expressed as number of elements.

4. resize() – Resizes the container so that it contains ‘g’ elements.

5. empty() – Returns whether the container is empty.

6. shrink_to_fit() – Reduces the capacity of the container to fit its size and destroys all elements beyond the capacity.

7. reserve() – Requests that the vector capacity be at least enough to contain n elements.

// C++ program to illustrate the 
// capacity function in vector 
#include <iostream> 
#include <vector> 

using namespace std; 

int main() 
{ 
	vector<int> g1; 

	for (int i = 1; i <= 5; i++) 
		g1.push_back(i); 

	cout << "Size : " << g1.size(); 
	cout << "\nCapacity : " << g1.capacity(); 
	cout << "\nMax_Size : " << g1.max_size(); 

	// resizes the vector size to 4 
	g1.resize(4); 

	// prints the vector size after resize() 
	cout << "\nSize : " << g1.size(); 

	// checks if the vector is empty or not 
	if (g1.empty() == false) 
		cout << "\nVector is not empty"; 
	else
		cout << "\nVector is empty"; 

	// Shrinks the vector 
	g1.shrink_to_fit(); 
	cout << "\nVector elements are: "; 
	for (auto it = g1.begin(); it != g1.end(); it++) 
		cout << *it << " "; 

	return 0; 
} 

Output:

Size : 5
Capacity : 8
Max_Size : 4611686018427387903
Size : 4
Vector is not empty
Vector elements are: 1 2 3 4

Element access:

1. reference operator [g] – Returns a reference to the element at position ‘g’ in the vector

2. at(g) – Returns a reference to the element at position ‘g’ in the vector

3. front() – Returns a reference to the first element in the vector

4. back() – Returns a reference to the last element in the vector

5. data() – Returns a direct pointer to the memory array used internally by the vector to store its owned elements.

// C++ program to illustrate the 
// element accesser in vector 
#include <bits/stdc++.h> 
using namespace std; 

int main() 
{ 
	vector<int> g1; 

	for (int i = 1; i <= 10; i++) 
		g1.push_back(i * 10); 

	cout << "\nReference operator [g] : g1[2] = " << g1[2]; 

	cout << "\nat : g1.at(4) = " << g1.at(4); 

	cout << "\nfront() : g1.front() = " << g1.front(); 

	cout << "\nback() : g1.back() = " << g1.back(); 

	// pointer to the first element 
	int* pos = g1.data(); 

	cout << "\nThe first element is " << *pos; 
	return 0; 
} 

Output:

Reference operator [g] : g1[2] = 30
at : g1.at(4) = 50
front() : g1.front() = 10
back() : g1.back() = 100
The first element is 10

Modifiers:

1. assign() – It assigns new value to the vector elements by replacing old ones

2. push_back() – It push the elements into a vector from the back

3. pop_back() – It is used to pop or remove elements from a vector from the back.

4. insert() – It inserts new elements before the element at the specified position

5. erase() – It is used to remove elements from a container from the specified position or range.

6. swap() – It is used to swap the contents of one vector with another vector of same type and size.

7. clear() – It is used to remove all the elements of the vector container

8. emplace() – It extends the container by inserting new element at position

9. emplace_back() – It is used to insert a new element into the vector container, the new element is added to the end of the vector

// C++ program to illustrate the 
// Modifiers in vector 
#include <bits/stdc++.h> 
#include <vector> 
using namespace std; 

int main() 
{ 
	// Assign vector 
	vector<int> v; 

	// fill the array with 10 five times 
	v.assign(5, 10); 

	cout << "The vector elements are: "; 
	for (int i = 0; i < v.size(); i++) 
		cout << v[i] << " "; 

	// inserts 15 to the last position 
	v.push_back(15); 
	int n = v.size(); 
	cout << "\nThe last element is: " << v[n - 1]; 

	// removes last element 
	v.pop_back(); 

	// prints the vector 
	cout << "\nThe vector elements are: "; 
	for (int i = 0; i < v.size(); i++) 
		cout << v[i] << " "; 

	// inserts 5 at the beginning 
	v.insert(v.begin(), 5); 

	cout << "\nThe first element is: " << v[0]; 

	// removes the first element 
	v.erase(v.begin()); 

	cout << "\nThe first element is: " << v[0]; 

	// inserts at the beginning 
	v.emplace(v.begin(), 5); 
	cout << "\nThe first element is: " << v[0]; 

	// Inserts 20 at the end 
	v.emplace_back(20); 
	n = v.size(); 
	cout << "\nThe last element is: " << v[n - 1]; 

	// erases the vector 
	v.clear(); 
	cout << "\nVector size after erase(): " << v.size(); 

	// two vector to perform swap 
	vector<int> v1, v2; 
	v1.push_back(1); 
	v1.push_back(2); 
	v2.push_back(3); 
	v2.push_back(4); 

	cout << "\n\nVector 1: "; 
	for (int i = 0; i < v1.size(); i++) 
		cout << v1[i] << " "; 

	cout << "\nVector 2: "; 
	for (int i = 0; i < v2.size(); i++) 
		cout << v2[i] << " "; 

	// Swaps v1 and v2 
	v1.swap(v2); 

	cout << "\nAfter Swap \nVector 1: "; 
	for (int i = 0; i < v1.size(); i++) 
		cout << v1[i] << " "; 

	cout << "\nVector 2: "; 
	for (int i = 0; i < v2.size(); i++) 
		cout << v2[i] << " "; 
} 

Output:

The vector elements are: 10 10 10 10 10 
The last element is: 15
The vector elements are: 10 10 10 10 10 
The first element is: 5
The first element is: 10
The first element is: 5
The last element is: 20
Vector size after erase(): 0

Vector 1: 1 2 
Vector 2: 3 4 
After Swap 
Vector 1: 3 4 
Vector 2: 1 2

All Vector Functions :

• vector::begin() and vector::end()

• vector rbegin() and rend()

• vector::cbegin() and vector::cend()

• vector::crend() and vector::crbegin()

• vector::assign()

• vector::at()

• vector::back()

• vector::capacity()

• vector::clear()

• vector::push_back()

• vector::pop_back()

• vector::empty()

• vector::erase()

• vector::size()

• vector::swap()

• vector::reserve()

• vector::resize()

• vector::shrink_to_fit()

• vector::operator=

• vector::operator[]

• vector::front()

• vector::data()

• vector::emplace_back()

• vector::emplace()

• vector::max_size()

• vector::insert()