Q156790: INFO: STL Sample for the operator == and operato

Article: Q156790
Product(s): Microsoft C Compiler
Version(s): 4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbcode kbVC420 kbVC500 kbVC600 kbDSupport
Last Modified: 27-MAR-2002

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The information in this article applies to:

- 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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NOTE: Microsoft Visual C++ NET (2002) supported both the managed code model that is provided by the .NET Framework and the unmanaged native Windows code model. The information in this article applies to unmanaged Visual C++ code only.

SUMMARY
=======

The sample code below illustrates how to use the operator== and operator< STL
functions for the deque container class in Visual C++.

MORE INFORMATION
================

Required Header
---------------

     < deque>

Prototype
---------

     template<class T, class A>

         bool operator==(
             const deque <T, A>& lhs,
             const deque <T, A>& rhs);

     template<class T, class A>

         bool operator<(
             const deque <T, A>& lhs,
             const deque <T, A>& rhs);

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 first template function overloads operator== to compare two objects of
template class deque. The function returns:

     lhs.size() == rhs.size() && equal(lhs. begin(), lhs. end(),
     rhs.begin()).

For equality, the number of elements must be equal in both the deque objects.

The second template function overloads operator< to compare two objects of
template class deque. The function returns:

     lexicographical_compare(lhs. begin(), lhs. end(), rhs.begin(),
     rhs.end()).

Because lexicographic (as in a dictionary) compare is used, the number of
elements does not matter while using operator<. In the sample code, adding a
line of code while creating the b object, such as b.push_front('D');, will make
b greater than a.

Sample Code
-----------

     ////////////////////////////////////////////////////////////////////// 
     // 
     // Compile options needed: -GX
     // 
     // deque.cpp :
     // 
     // Functions:
     // 
     //    ==
     //    <
     // 
     // Written by Bobby Mattappally
     // of Microsoft Product Support Services,
     // Copyright (c) 1996 Microsoft Corporation. All rights reserved.
     ////////////////////////////////////////////////////////////////////// 

     /* Compile options needed:-GX
     */ 
     #include <iostream>
     #include <deque>
     
  #if _MSC_VER > 1020   // if VC++ version is > 4.2
     using namespace std;  // std c++ libs implemented in std
     #endif

     typedef deque<char, allocator<char> >  CHARDEQUE;
     void print_contents (CHARDEQUE  deque, char*);

     void main()
     {
         //create a  with  3 A's
         CHARDEQUE  a(3,'A');
         a.push_front('C');

         //create b with 4 B's.
         CHARDEQUE  b(6,'B');

         //print out the contents
         print_contents (a,"a");
         print_contents (b,"b");

         //compare a and b
         if (a==b)
             cout <<"a is equal to b"<<endl;
         else if(a<b)
                 cout <<"a is less than b"<<endl;
         else
             cout <<"a is greater than b" <<endl;

         //assign the contents of b to a
         a.assign(b.begin(),b.end());
         print_contents (a,"a");
         print_contents (b,"b");

         //compare a and b again
         if (a==b)
             cout <<"a is equal to b"<<endl;
         else if(a<b)
                 cout <<"a is less than b"<<endl;
         else
             cout <<"a is greater than b" <<endl;

     }

     //function to print the contents of deque
     void print_contents (CHARDEQUE  deque, char *name)
     {
         CHARDEQUE::iterator pdeque;

         cout <<"The contents of "<< name <<" : ";

             for(pdeque = deque.begin();
             pdeque != deque.end();
             pdeque++)
         {
             cout << *pdeque <<" " ;
         }
             cout<<endl;

     }

Program output is:

  The contents of a : C A A A
  The contents of b : B B B B B B
  a is greater than b
  The contents of a : B B B B B B
  The contents of b : B B B B B B
  a is equal to b

REFERENCES
==========

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.

Additional query words: STL STLSample deque == kbSTL kbtemplate

======================================================================
Keywords          : kbcode kbVC420 kbVC500 kbVC600 kbDSupport 
Technology        : kbVCsearch kbAudDeveloper kbVC420 kbVC500 kbVC600 kbVC32bitSearch kbVCNET kbVC500Search
Version           : :4.2,5.0,6.0
Issue type        : kbinfo

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