How to traverse stack in C++?

It is not possible to directly traverse an std:: stack as it does not have an end member and that's how a stack data-structure is supposed to be i.e. only have one pointer. But, still here are two lazy hacks to traverse it:

1) Loop Based:

while(!st.empty()) {
        cout << st.top();
        st.pop();
    }

Problems with the loop-based approach:

• The original stack gets empty.

2) Recursion Based:

template <typename T>
void traverse_stack(stack<T> & st) {
    if(st.empty())
        return;
    T x = st.top();
    cout << x << " ";
    st.pop();
    traverse_stack(st);
    st.push(x);
}

Advantages of Recursion based approach:

• Maintains the original stack elements.

Problems with Recursion based approach:

• Maintains an internal stack.
• May fail for large size of the stack.

Is it possible to traverse std::stack in C++?

No. A stack is a data structure you should use when you are interested in placing elements on top and getting elements from the top. If you want an iterable stack, either use a different data structure for a stack role (std::vector?) or write one yourself.

As you mentioned you need printing for debugging purposes, maybe something like this would work for you:

// Example program
#include <iostream>
#include <string>
#include <stack>
#include <vector>
#include <algorithm>

template <typename T>
void StackDebug(std::stack<T> s)
{
    std::vector<T> debugVector = std::vector<T>();
    while (!s.empty( ) )
    {
        T t = s.top( );
        debugVector.push_back(t);
        s.pop( );
    }

    // stack, read from top down, is reversed relative to its creation (from bot to top)
    std::reverse(debugVector.begin(), debugVector.end());
    for(const auto& it : debugVector)
    {
        std::cout << it << " ";
    }
}

int main()
{

    std::stack< int > numbers;
    numbers.push( 9 );
    numbers.push( 11 );

    StackDebug(numbers);
}

Output is, as expected, "9 11"