deque::operator== and deque::operator<
Illustrates how to use the deque::operator== and deque::operator< Standard Template Library (STL) functions in Visual C++.
template<class T, class A>
bool operator==(
const deque <T, A>& Left,
const deque <T, A>& Right
);
template<class T, class A>
bool operator<(
const deque <T, A>& Left,
const deque <T, A>& Right
);
Remarks
备注
The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.
The first template function overloads operator== to compare two objects of template class deque. The function returns Left.size == Right.size && equal(Left.begin, Left.end, Right.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(Left.begin, Left.end, Right.begin, Right.end). Because lexicographical_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.
Example
// deque_operators.cpp
// compile with: /EHsc
//
// Functions:
// ==
// <
#include <iostream>
#include <deque>
using namespace std;
typedef deque<char > CHARDEQUE;
void print_contents (CHARDEQUE deque, char*);
int 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;
}
Output
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
Requirements
Header: <deque>