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deque::operator[] and deque::at 

Illustrates how to use the deque::operator[] and deque::at Standard Template Library (STL) functions in Visual C++.


const_reference operator[](
   size_type Pos
) const;
reference operator[](
   size_type Pos
);
const_reference operator[](
   difference_type _N
) const;
reference operator[](
   difference_type _N
) const;
const_reference at(
   size_type Pos
) const;
reference at(
   size_type Pos
); bool empty( ) const;

NoteNote

The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.

The operator[] member function returns a reference to the element of the controlled sequence at position Pos. If that position is invalid, the behavior is undefined. The at member function returns a reference to the element of the controlled sequence at position Pos. If that position is invalid, the function throws an object of class out_of_range. The empty member function returns true for an empty controlled sequence.

// operator.cpp
// compile with: /EHsc
//
// Functions:
//    operator[]
//    at
//    empty
//    push_back
//    begin
//    end

#include <iostream>
#include <deque>

using namespace std;


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

int main()
{
    //create an empty deque a
    CHARDEQUE  a;

    //check whether it is empty
    if(a.empty())
        cout<<"a is empty"<<endl;
    else
        cout<<"a is not empty"<<endl;

    //inset A, B, C and D  to a
    a.push_back('A');
    a.push_back('B');
    a.push_back('C');
    a.push_back('D');

    //check again whether a is empty
    if(a.empty())
        cout<<"a is empty"<<endl;
    else
        cout<<"a is not empty"<<endl;

    //print out the contents

    print_contents (a,"a");

    cout <<"The first element of a is " <<a[0] <<endl;
    cout <<"The first element of a is " <<a.at(0) <<endl;

    cout <<"The last element of a is " <<a[a.size()-1] <<endl;
    cout <<"The last element of a is " <<a.at(a.size()-1) <<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

a is empty
a is not empty
The contents of a : A B C D
The first element of a is A
The first element of a is A
The last element of a is D
The last element of a is D

Header: < deque>

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