How to access the back data from queue in C++ with user defined function?

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C++

I need to access back data from queue in C++ through linked list implementation.
I used STL::back function for this.

#include <iostream>  
#include <queue>  
int main()  
{  
    std::queue<int> myQ;  
    myQ.push(10);  
    myQ.push(20); 
    myQ.push(30);  
    myQ.push(40);
    std::cout <<"newqueue.back():  "<< myQ.back ();  
    return 0;  
}

What I have tried:

I have tried STL back function.

#include <iostream>
#include <queue>
int main()
{
std::queue<int> myQ;
myQ.push(10);
myQ.push(20);
myQ.push(30);
myQ.push(40);
std::cout <<"newqueue.back(): "<< myQ.back ();
return 0;
}