How can I print out the contents of std::stack and return its size?

Question

In c++ how can I print out the contents of my stack and return its size?

std::stack<int>  values;
values.push(1);
values.push(2);
values.push(3);

// How do I print the stack?

Answer 1

Both std::stack and std::queue are wrappers around a general container. That container is accessible as the protected member c. Using c you can gain efficient access to the elements; otherwise, you can just copy the stack or queue and destructively access the elements of the copy.

Example of using c:

#include <iostream>     // std::wcout, std::endl
#include <stack>        // std::stack
#include <stddef.h>     // ptrdiff_t
using namespace std;

typedef ptrdiff_t   Size;
typedef Size        Index;

template< class Elem >
Size nElements( stack< Elem > const& c )
{
    return c.size();
}

void display( stack<int> const& numbers )
{
    struct Hack
        : public stack<int>
    {
        static int item( Index const i, stack<int> const& numbers )
        {
            return (numbers.*&Hack::c)[i];
        }
    };

    wcout << numbers.size() << " numbers." << endl;
    for( Index i = 0;  i < nElements( numbers );  ++i )
    {
        wcout << "  " << Hack::item( i, numbers ) << endl;
    }
}

int main()
{
    stack<int>  numbers;
    for( int i = 1;  i <= 5;  ++i ) { numbers.push( 100*i ); }

    display( numbers );
}