vector::front and vector::back (STL Sample)

The sample code below illustrates how to use the vector::front and vector::back STL functions in Visual C++.

Required Header:
<vector>

template<class _TYPE, class _A>
    reference vector::front();

template<class _TYPE, class _A>
    reference vector::back();

Note: The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.

Description:
The sample declares an empty vector of integers with the members [100, 200, 300, 400]. It displays the first element of the vector using vector::front to obtain it. It displays the last element of the vector using vector::back to obtain it. It displays the number of elements of the vector using vector::size. The sample erases the last element of the vector using vector::end()-1, and then displays the new last element using vector::back. It erases the first element of the vector using vector::begin, and then displays the new first element using vector::front. Finally, the sample displays the number of elements remaining in the vector using vector::size.

Sample Code:

//////////////////////////////////////////////////////////////////////
//
// Compile options needed: /GX
//
//    front.cpp: Illustrates the vector::front and vector::back methods.
//
// Functions:
//
//    vector::front - Returns reference to first element of vector.
//
//    vector::back - Returns reference to last element of vector.
//
//    vector::push_back - Appends (inserts) an element to the end of a
//                        vector, allocating memory for it if necessary.
//
//    vector::size - Returns number of elements in the vector.
//
//    vector::begin - Returns an iterator to start traversal of the vector.
//
//    vector::end - Returns an iterator for the last element of the vector.
//
//    vector::erase - Deletes elements from a vector (single & range).
//
//////////////////////////////////////////////////////////////////////

// The debugger can't handle symbols more than 255 characters long.
// STL often creates symbols longer than that.
// When symbols are longer than 255 characters, the warning is issued.
#pragma warning(disable:4786)

#include <iostream>
#include <vector>

using namespace std ;

typedef vector<int> INTVECTOR;

const ARRAY_SIZE = 4;

void main()
{
    // Dynamically allocated vector begins with 0 elements.
    INTVECTOR theVector;

    // Intialize the array to contain the members [100, 200, 300, 400]
    for (int cEachItem = 0; cEachItem < ARRAY_SIZE; cEachItem++)
        theVector.push_back((cEachItem + 1) * 100);

    cout << "First element: " << theVector.front() << endl;
    cout << "Last element: " << theVector.back() << endl;
    cout << "Elements in vector: " << theVector.size() << endl;

    // Delete the last element of the vector. Remember that the vector
    // is 0-based, so theVector.end() actually points 1 element beyond
    // the end.
    theVector.erase(theVector.end() - 1);

    cout << endl << "After erasing last element, new last element is: "
         << theVector.back() << endl;

    // Delete the first element of the vector.
    theVector.erase(theVector.begin());

    cout << "After erasing first element, new first element is: "
         << theVector.front() << endl;

    cout << "Elements in vector: " << theVector.size() << endl;
}

 

Program Output is:

First element: 100
Last element: 400
Elements in vector: 4

After erasing last element, new last element is: 300
After erasing first element, new first element is: 200
Elements in vector: 2