INFO: STL Sample for the stack::top and stack::empty Functions

ID: Q158040

The information in this article applies to:

The Standard C++ Library, used with:
- Microsoft Visual C++, 32-bit Editions, versions 4.2, 5.0, 6.0

SUMMARY

The sample code below illustrates how to use the stack::top and stack::empty STL functions in Visual C++.

MORE INFORMATION

Required Header


   <stack>

Prototype


    template<class _TYPE, class _C, class _A>    // Function 1
    value_type& stack::top();

    template<class _TYPE, class _C, class _A>    // Function 2
    const value_type& stack::top() const;

    template<class _TYPE, class _C, class _A>    // Function 3
    bool stack::empty() const;

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

Description

The top function returns the topmost element of the stack. You should ensure that there are one or more elements on the stack before calling the top function. The first version of the top function returns a reference to the element of the top of the stack, allowing you to modify the value. The second function returns a constant reference, ensuring that you don't accidentally modify the stack.

The empty function returns true if there are no elements in the stack. If there are one or more elements, the function will return false. You should use the empty function to verify that there are elements left on the stack before calling the top function.

Sample Code


////////////////////////////////////////////////////////////////////// 
// 
// Compile options needed: /GX
// 
// StackTop&Empty.cpp : Illustrates how to use the top function to
//                      retrieve the last element of the controlled
//                      sequence. It also illustrates how to use the
//                      empty function to loop though the stack.
// Functions:
// 
//    top   :  returns the top element of the stack.
//    empty :  returns true if the stack has 0 elements.
// 
// Written by Derek Jamison
// of Microsoft Product Support Services,
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
////////////////////////////////////////////////////////////////////// 

#pragma warning(disable:4786)

#include <stack>
#include <iostream>

#if _MSC_VER > 1020   // if VC++ version is > 4.2
   using namespace std;  // std c++ libs implemented in std
   #endif

typedef stack<int,  deque<int,allocator<int> >,  allocator<int> >

        STACK_INT;


void main()

{

   STACK_INT stack1;

   cout << "stack1.empty() returned " <<

      (stack1.empty()? "true": "false") << endl;  // Function 3

   cout << "stack1.push(2)" << endl;
   stack1.push(2);

   if (!stack1.empty())                           // Function 3

      cout << "stack1.top() returned " <<
      stack1.top() << endl;                       // Function 1

   cout << "stack1.push(5)" << endl;
   stack1.push(5);

   if (!stack1.empty())                           // Function 3

      cout << "stack1.top() returned " <<
      stack1.top() << endl;                       // Function 1

   cout << "stack1.push(11)" << endl;
   stack1.push(11);

   if (!stack1.empty())                           // Function 3

      cout << "stack1.top() returned " <<
      stack1.top() << endl;                       // Function 1

   // Modify the top item. Set it to 6.
   if (!stack1.empty()) {                         // Function 3
      cout << "stack1.top()=6;" << endl;
      stack1.top()=6;                             // Function 1
   }

   // Repeat until stack is empty
   while (!stack1.empty()) {                      // Function 3
      const int& t=stack1.top();                  // Function 2
      cout << "stack1.top() returned " << t << endl;
      cout << "stack1.pop()" << endl;
      stack1.pop();
   }

}

Program Output is:


stack1.empty() returned true
stack1.push(2)
stack1.top() returned 2
stack1.push(5)
stack1.top() returned 5
stack1.push(11)
stack1.top() returned 11
stack1.top()=6;
stack1.top() returned 6
stack1.pop()
stack1.top() returned 5
stack1.pop()
stack1.top() returned 2
stack1.pop()

REFERENCES

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.

Additional query words: STL STLSample top empty

Keywords : kbcode kbVC420 kbVC500 kbVC600 kbDSupport STLIss
Version : winnt:4.2,5.0,6.0
Platform : winnt
Issue type : kbinfo