The sample code below illustrates how to use the stack::top
and stack::empty STL functions in Visual C++.
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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;
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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For more information about stack::top and stack::empty, visit
the following Microsoft Developer Network (MSDN) Web site:
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