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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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);
: 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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For the same information about the operator == and the operator
<, visit the following Microsoft Developer Network (MSDN) Web site:
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