INFO: (front, back) Functions

ID: Q158613

The information in this article applies to:

The Standard C++ Library, used with:
- Microsoft Visual C++, 32-bit Editions, versions 4.2, 5.0, 6.0

SUMMARY

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

MORE INFORMATION

Required Header


   <vector>

Prototypes


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

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

NOTE: The class/parameter names in the prototype may 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).
// 
// Written by Tom Campbell
// of Microsoft Corporation
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
////////////////////////////////////////////////////////////////////// 

// 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>

#if _MSC_VER > 1020   // if VC++ version is > 4.2
   using namespace std;  // std c++ libs implemented in std
   #endif

typedef vector<int, allocator<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


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

REFERENCES

Visual C++ Books Online: Visual C++ Books; C/C++; Standard C++ Library Reference

Additional query words: STL STLSample

Keywords : kbcode kbVC420 kbVC500 kbVC600 kbDSupport STLIss
Version : winnt:4.2,5.0,6.0
Platform : winnt
Issue type : kbinfo