DOCUMENT:Q158613  27-MAR-2002  [visualc]
TITLE   :STL Sample for the vector::(front, back) Functions
PRODUCT :Microsoft C Compiler
PROD/VER::4.2,5.0,6.0
OPER/SYS:
KEYWORDS:kbcode kbtemplate kbSTL kbVC420 kbVC500 kbVC600 kbDSupport

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The information in this article applies to:

 - The Standard C++ Library, used with:
    - Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 5.0, 6.0 
    - Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 5.0, 6.0 
    - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
    - Microsoft Visual C++.NET (2002) 
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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
-----------

NOTE: The first line in the sample code section says:

   // Compile options needed: /GX

In VC++ .NET, /EHsc is set by default and is equivalent to /GX.

   ////////////////////////////////////////////////////////////////////// 
   // 
   // 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)

   // disable warning C4267: possible loss of data,
   // okay to ignore

   #pragma warning(disable: 4267)

   #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 kbtemplate kbSTL kbVC420 kbVC500 kbVC600 kbDSupport 
Technology        : kbVCsearch kbAudDeveloper kbVCLibrary
Version           : :4.2,5.0,6.0
Issue type        : kbinfo

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