Article ID: 156790 - Last Review: January 11, 2006 - Revision: 6.0

How to use the operator == and the operator < Standard Template Library (STL) functions for the deque container class in Visual C++

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This article was previously published under Q156790
Note Microsoft Visual C++ .NET 2002 and Microsoft Visual C++ .NET 2003 support both the managed code model that is provided by the Microsoft .NET Framework and the unmanaged native Microsoft Windows code model. The information in this article applies only to unmanaged Visual C++ code. Microsoft Visual C++ 2005 supports both the managed code model that is provided by the Microsoft .NET Framework and the unmanaged native Microsoft Windows code model.

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SUMMARY

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

Required Header

   < deque>
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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.
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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.
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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
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REFERENCES

For the same information about the operator == and the operator <, visit the following Microsoft Developer Network (MSDN) Web site:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vcstdlib/html/vcsampsampleoperatoreeandoperatorldequestlsample.asp (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vcstdlib/html/vcsampsampleoperatoreeandoperatorldequestlsample.asp)
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APPLIES TO
  • Microsoft Visual C++ 4.2 Enterprise Edition
  • Microsoft Visual C++ 5.0 Enterprise Edition
  • Microsoft Visual C++ 6.0 Enterprise Edition
  • Microsoft Visual C++ 4.2 Professional Edition
  • Microsoft Visual C++ 5.0 Professional Edition
  • Microsoft Visual C++ 6.0 Professional Edition
  • Microsoft Visual C++, 32-bit Learning Edition 6.0
  • Microsoft Visual C++ 2005 Express Edition
  • Microsoft Visual C++ .NET 2003 Standard Edition
  • Microsoft Visual C++ .NET 2002 Standard Edition
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Keywords: 
kbhowto kbinfo kbcode kbfunctions KB156790
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