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stack Class

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The latest version of this topic can be found at stack Class.

A template container adaptor class that provides a restriction of functionality limiting access to the element most recently added to some underlying container type. The stack class is used when it is important to be clear that only stack operations are being performed on the container.

Syntax

template <class Type, class Container= deque <Type>>  
class stack

Parameters

Type
The element data type to be stored in the stack.

Container
The type of the underlying container used to implement the stack. The default value is the class deque<Type>.

Remarks

The elements of class Type stipulated in the first template parameter of a stack object are synonymous with value_type and must match the type of element in the underlying container class Container stipulated by the second template parameter. The Type must be assignable, so that it is possible to copy objects of that type and to assign values to variables of that type.

Suitable underlying container classes for stack include deque, list class, and vector class, or any other sequence container that supports the operations of back, push_back, and pop_back. The underlying container class is encapsulated within the container adaptor, which exposes only the limited set of the sequence container member functions as a public interface.

The stack objects are equality comparable if and only if the elements of class Type are equality comparable and are less-than comparable if and only if the elements of class Type are less-than comparable.

  • The stack class supports a last-in, first-out (LIFO) data structure. A good analogue to keep in mind would be a stack of plates. Elements (plates) may be inserted, inspected, or removed only from the top of the stack, which is the last element at the end of the base container. The restriction to accessing only the top element is the reason for using the stack class.

  • The queue class supports a first-in, first-out (FIFO) data structure. A good analogue to keep in mind would be people lining up for a bank teller. Elements (people) may be added to the back of the line and are removed from the front of the line. Both the front and the back of a line may be inspected. The restriction to accessing only the front and back elements in this way is the reason fur using the queue class.

  • The priority_queue class orders its elements so that the largest element is always at the top position. It supports insertion of an element and the inspection and removal of the top element. A good analogue to keep in mind would be people lining up where they are arranged by age, height, or some other criterion.

Constructors

stack Constructs a stack that is empty or that is a copy of a base container object.

Typedefs

container_type A type that provides the base container to be adapted by a stack.
size_type An unsigned integer type that can represent the number of elements in a stack.
value_type A type that represents the type of object stored as an element in a stack.

Member Functions

empty Tests if the stack is empty.
pop Removes the element from the top of the stack.
push Adds an element to the top of the stack.
size Returns the number of elements in the stack.
top Returns a reference to an element at the top of the stack.

Requirements

Header: <stack>

Namespace: std

stack::container_type

A type that provides the base container to be adapted.

typedef Container container_type;

Remarks

The type is a synonym for the template parameter Container. All three STL sequence container classes — the vector class, list class, and the default class deque — meet the requirements to be used as the base container for a stack object. User-defined types satisfying these requirements may also be used.

For more information on Container, see the Remarks section of the stack Class topic.

Example

See the example for stack::stack for an example of how to declare and use container_type.

stack::empty

Tests if a stack is empty.

bool empty() const;

Return Value

true if the stack is empty; false if the stack is nonempty.

Example

// stack_empty.cpp  
// compile with: /EHsc  
#include <stack>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
   // Declares stacks with default deque base container  
   stack <int> s1, s2;  
  
   s1.push( 1 );  
  
   if ( s1.empty( ) )  
      cout << "The stack s1 is empty." << endl;  
   else  
      cout << "The stack s1 is not empty." << endl;  
  
   if ( s2.empty( ) )  
      cout << "The stack s2 is empty." << endl;  
   else  
      cout << "The stack s2 is not empty." << endl;  
}  

The stack s1 is not empty.  
The stack s2 is empty.

stack::pop

Removes the element from the top of the stack.

void pop();

Remarks

The stack must be nonempty to apply the member function. The top of the stack is the position occupied by the most recently added element and is the last element at the end of the container.

Example

// stack_pop.cpp  
// compile with: /EHsc  
#include <stack>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
   stack <int> s1, s2;  
  
   s1.push( 10 );  
   s1.push( 20 );  
   s1.push( 30 );  
  
   stack <int>::size_type i;  
   i = s1.size( );  
   cout << "The stack length is " << i << "." << endl;  
  
   i = s1.top( );  
   cout << "The element at the top of the stack is "  
        << i << "." << endl;  
  
   s1.pop( );  
  
   i = s1.size( );  
   cout << "After a pop, the stack length is "   
        << i << "." << endl;  
  
   i = s1.top( );  
   cout << "After a pop, the element at the top of the stack is "  
        << i << "." << endl;  
}  

The stack length is 3.  
The element at the top of the stack is 30.  
After a pop, the stack length is 2.  
After a pop, the element at the top of the stack is 20.

stack::push

Adds an element to the top end of the stack.

void push(const Type& val);

Parameters

val
The element added to the top of the stack.

Remarks

The top of the stack is the position occupied by the most recently added element and is the last element at the end of the container.

Example

// stack_push.cpp  
// compile with: /EHsc  
#include <stack>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
   stack <int> s1;  
  
   s1.push( 10 );  
   s1.push( 20 );  
   s1.push( 30 );  
  
   stack <int>::size_type i;  
   i = s1.size( );  
   cout << "The stack length is " << i << "." << endl;  
  
   i = s1.top( );  
   cout << "The element at the top of the stack is "  
        << i << "." << endl;  
}  

The stack length is 3.  
The element at the top of the stack is 30.

stack::size

Returns the number of elements in the stack.

size_type size() const;

Return Value

The current length of the stack.

Example

// stack_size.cpp  
// compile with: /EHsc  
#include <stack>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
   stack <int> s1, s2;  
   stack <int>::size_type i;  
  
   s1.push( 1 );  
   i = s1.size( );  
   cout << "The stack length is " << i << "." << endl;  
  
   s1.push( 2 );  
   i = s1.size( );  
   cout << "The stack length is now " << i << "." << endl;  
}  

The stack length is 1.  
The stack length is now 2.

stack::size_type

An unsigned integer type that can represent the number of elements in a stack.

typedef typename Container::size_type size_type;

Remarks

The type is a synonym for size_type of the base container adapted by the stack.

Example

See the example for size for an example of how to declare and use size_type.

stack::stack

Constructs a stack that is empty or that is a copy of a base container class.

stack();

explicit stack(const container_type& right);

Parameters

right
The container of which the constructed stack is to be a copy.

Example

// stack_stack.cpp  
// compile with: /EHsc  
#include <stack>  
#include <vector>  
#include <list>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
  
   // Declares stack with default deque base container  
   stack <char> dsc1;  
  
   //Explicitly declares a stack with deque base container  
   stack <char, deque<char> > dsc2;  
  
   // Declares a stack with vector base containers  
   stack <int, vector<int> > vsi1;  
  
   // Declares a stack with list base container  
   stack <int, list<int> > lsi;  
  
   // The second member function copies elements from a container  
   vector<int> v1;  
   v1.push_back( 1 );  
   stack <int, vector<int> > vsi2( v1 );  
   cout << "The element at the top of stack vsi2 is "  
        << vsi2.top( ) << "." << endl;  
}  

The element at the top of stack vsi2 is 1.

stack::top

Returns a reference to an element at the top of the stack.

reference top();

const_reference top() const;

Return Value

A reference to the last element in the container at the top of the stack.

Remarks

The stack must be nonempty to apply the member function. The top of the stack is the position occupied by the most recently added element and is the last element at the end of the container.

If the return value of top is assigned to a const_reference, the stack object cannot be modified. If the return value of top is assigned to a reference, the stack object can be modified.

Example

// stack_top.cpp  
// compile with: /EHsc  
#include <stack>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
   stack <int> s1;  
  
   s1.push( 1 );  
   s1.push( 2 );  
  
   int& i = s1.top( );  
   const int& ii = s1.top( );  
  
   cout << "The top integer of the stack s1 is "  
        << i << "." << endl;  
   i--;  
   cout << "The next integer down is "<< ii << "." << endl;  
}  

The top integer of the stack s1 is 2.  
The next integer down is 1.

stack::value_type

A type that represents the type of object stored as an element in a stack.

typedef typename Container::value_type value_type;

Remarks

The type is a synonym for value_type of the base container adapted by the stack.

Example

// stack_value_type.cpp  
// compile with: /EHsc  
#include <stack>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
   // Declares stacks with default deque base container  
   stack<int>::value_type AnInt;  
  
   AnInt = 69;  
   cout << "The value_type is AnInt = " << AnInt << endl;  
  
   stack<int> s1;  
   s1.push( AnInt );  
   cout << "The element at the top of the stack is "  
        << s1.top( ) << "." << endl;  
}  

The value_type is AnInt = 69  
The element at the top of the stack is 69.

See Also

Thread Safety in the C++ Standard Library
Standard Template Library