C++ <deque> - operator=() Function

The C++ deque::operator= function is used to assign new content to the container by replacing the current content and adjusting the container size accordingly.

Syntax

C++98
C++11

//copies all elements of x into the container
deque& operator= (const deque& x);

//copy version - copies all elements
//of x into the container
deque& operator= (const deque& x);

//move version - moves elements of x
//into the container
deque& operator= (deque&& x);

//initializer list version - copies all 
//elements of il into the container
deque& operator= (initializer_list<value_type> il);

Parameters

`x`	Specify a deque object of same type.
`il`	Specify an initializer_list object.

Return Value

Returns *this.

Time Complexity

Linear i.e, Θ(n).

Example: using copy version

In the example below, the deque::operator= function is used to assign new values to the given deque.

#include <iostream>
#include <deque>
using namespace std;
 
int main (){
  deque<int> dq1{10, 20, 30, 40, 50};

  //copying all content of dq1 into dq2
  deque<int> dq2;
  dq2 = dq1;

  cout<<"The dq1 contains:";
  for(int i = 0; i < dq1.size(); i++)
    cout<<" "<<dq1[i];

  cout<<"\nThe dq2 contains:";
  for(int i = 0; i < dq2.size(); i++)
    cout<<" "<<dq2[i];

  return 0;
}

The output of the above code will be:

The dq1 contains: 10 20 30 40 50
The dq2 contains: 10 20 30 40 50

Example: using move version

Using the move version of operator=, the content of one deque can be moved to another deque. Consider the following example:

#include <iostream>
#include <deque>
using namespace std;
 
int main (){
  deque<int> dq1{10, 20, 30, 40, 50};

  cout<<"The dq1 contains:";
  for(int i = 0; i < dq1.size(); i++)
    cout<<" "<<dq1[i];

  //moving all content of dq1 into dq2
  deque<int> dq2;
  dq2 = move(dq1);

  cout<<"\nThe dq1 contains:";
  for(int i = 0; i < dq1.size(); i++)
    cout<<" "<<dq1[i];

  cout<<"\nThe dq2 contains:";
  for(int i = 0; i < dq2.size(); i++)
    cout<<" "<<dq2[i];

  return 0;
}

The output of the above code will be:

The dq1 contains: 10 20 30 40 50
The dq1 contains:
The dq2 contains: 10 20 30 40 50

Example: using initializer list version

The initializer list can also be used to assign values into a deque container. Consider the example below:

#include <iostream>
#include <deque>
using namespace std;
 
int main (){
  //creating empty deque
  deque<int> dq;

  //creating initializer list
  initializer_list<int> ilist = {10, 20, 30, 40, 50};

  //assigning values of dq using ilist
  dq = ilist;

  cout<<"The dq contains:";
  for(int i = 0; i < dq.size(); i++)
    cout<<" "<<dq[i];

  return 0;
}

The output of the above code will be:

The dq contains: 10 20 30 40 50

❮ C++ <deque> Library