operator == and operator < deque (STL Sample)

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

Required Header:
< deque>

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 do 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 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:
//
//    ==
//    <
//
//////////////////////////////////////////////////////////////////////

/* Compile options needed:-GX
*/
#include <iostream>
#include <deque>

using namespace std;


typedef deque<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