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Article ID: 158040 - Last Review: July 12, 2005 - Revision: 4.1

How to use the stack::top and stack::empty STL functions in Visual C++

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This article was previously published under Q158040
Note Microsoft Visual C++ .NET 2002 and Microsoft Visual C++ .NET 2003 support both the managed code model that is provided by the Microsoft .NET Framework and the unmanaged native Microsoft Windows code model. The information in this article applies only to unmanaged Visual C++ code.

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SUMMARY

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

Required header

   <stack>
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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.
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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.
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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> > 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();
   }

}
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REFERENCES

For more information about stack::top and stack::empty, visit the following Microsoft Developer Network (MSDN) Web site:
http://msdn.microsoft.com/en-us/library/90t04h29.aspx (http://msdn.microsoft.com/en-us/library/90t04h29.aspx)
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APPLIES TO
  • The Standard C++ Library, when used with:
    • Microsoft Visual C++ 4.2 Enterprise Edition
    • Microsoft Visual C++ 5.0 Enterprise Edition
    • Microsoft Visual C++ 6.0 Enterprise Edition
    • Microsoft Visual C++ 4.2 Professional Edition
    • Microsoft Visual C++ 5.0 Professional Edition
    • Microsoft Visual C++ 6.0 Professional Edition
    • Microsoft Visual C++, 32-bit Learning Edition 6.0
    • Microsoft Visual C++ .NET 2002 Standard Edition
    • Microsoft Visual C++ .NET 2003 Standard Edition
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Keywords: 
kbhowto kbcode kbinfo kbstl kbtemplate KB158040
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