vector::begin() and vector::end() in C++ STL

Vectors are the same as dynamic arrays with the ability to resize itself automatically when an element is inserted or deleted, with their storage being handled automatically by the container.

vector::begin()

begin() function is used to return an iterator pointing to the first element of the vector container. begin() function returns a bidirectional iterator to the first element of the container.

Syntax :

vectorname.begin()

Parameters: No parameters are passed.

Return Type: 
This function returns a bidirectional
iterator pointing to the first element.

Examples: 

Input  : myvector{1, 2, 3, 4, 5};
         myvector.begin();
Output : returns an iterator to the element 1

Input  : myvector{"This", "is", "Geeksforgeeks"};
         myvector.begin();
Output : returns an iterator to the element This

Errors and Exceptions

• It has a no exception throw guarantee. 
• Shows error when a parameter is passed. 

CPP

// INTEGER VECTOR EXAMPLE
// CPP program to illustrate
// Implementation of begin() function
#include <iostream>
#include <vector>
using namespace std;

int main()
{
    // declaration of vector container
    vector<int> myvector{ 1, 2, 3, 4, 5 };

    // using begin() to print vector
    for (auto it = myvector.begin();
         it != myvector.end(); ++it)
        cout << ' ' << *it;
    return 0;
}

Output: 

1 2 3 4 5

CPP

// STRING VECTOR EXAMPLE
// CPP program to illustrate
// Implementation of begin() function
#include <iostream>
#include <string>
#include <vector>
using namespace std;

int main()
{
    // declaration of vector container
    vector<string> myvector{ "This", "is",
                             "Geeksforgeeks" };

    // using begin() to print vector
    for (auto it = myvector.begin();
         it != myvector.end(); ++it)
        cout << ' ' << *it;
    return 0;
}

Output: 

This is Geeksforgeeks

Time Complexity: O(1)

vector::end()

end() function is used to return an iterator pointing next to last element of the vector container. end() function returns a bidirectional iterator.

Syntax :

vectorname.end()

Parameters :
No parameters are passed.

Return Type:
This function returns a bidirectional
iterator pointing to next to last element.

Examples:

Input  : myvector{1, 2, 3, 4, 5};
         myvector.end();
Output : returns an iterator after 5

Input  : myvector{"computer", "science", "portal"};
         myvector.end();
Output : returns an iterator after portal

Errors and Exceptions

1. It has a no exception throw guarantee. 
2. Shows error when a parameter is passed.

CPP

// INTEGER VECTOR EXAMPLE
// CPP program to illustrate
// Implementation of end() function
#include <iostream>
#include <vector>
using namespace std;

int main()
{
    // declaration of vector container
    vector<int> myvector{ 1, 2, 3, 4, 5 };

    // using end() to print vector
    for (auto it = myvector.begin();
         it != myvector.end(); ++it)
        cout << ' ' << *it;
    return 0;
}

Output: 

1 2 3 4 5

CPP

// STRING VECTOR EXAMPLE
// CPP program to illustrate
// Implementation of end() function
#include <iostream>
#include <string>
#include <vector>
using namespace std;

int main()
{
    // declaration of vector container
    vector<string> myvector{ "computer", "science",
                             "portal" };

    // using end() to print vector
    for (auto it = myvector.begin(); it != myvector.end();
         ++it)
        cout << ' ' << *it;
    return 0;
}

Output: 

computer science portal

Time Complexity: O(1) 

Let us see the differences in a tabular form is as follows:

vector::begin()	vector::end()
It is used to return an iterator pointing to the first element in the vector.	It is used to return an iterator referring to the past-the-end element in the vector container.
Its syntax is -: iterator begin();	Its syntax is -: iterator end();
It does not take any parameters.	It does not take any parameters.
Its complexity is constant.	Its complexity is constant.
Its iterator validity does not change.	Its iterator validity does not change.