Container Adaptors

Notes from C++ Primer

stack and queue: based on deque
priority_queue: based on vector

Standard library provides three kinds of sequential adaptors: queue, priority_queue and stack. When we use adaptor, we must include the relevant head files:

1 2	`#include <stack>` `#include <queue> // both queue and priority_queue adaptors`

We can use two ways to initialize the adaptor: default constructor or a constructor with one container parameter:

1 2	`deque<int> deq;` `stack<int> stk(deq);` `// copies elements from deq into stk`

Also we can override the underlying container type by passing a sequential container type:

// empty stack implemented on top of vector
stack<string, vector<string> > str_stk;
 
// str_stk2 is implemented on top of vector and holds a copy of svec
stack<string, vector<string> > str_stk2(svec);

There're constraints on which containers can be used for a given adaptor.

stack: any sequential container: vector, list, deque

queue: the underlying container must support push_front, so only based on: list

priority_queue: the underlying container should support random access, so based on: vecotr or deque

Stack Adaptor Operation

s.empty() if the stack is empty, return true
s.size() return the size of elements in the stack
s.pop() delete the top element of stack, NOT return its value
s.top() return the value of top element in stack, not deleting
s.push(item) push new element in stack

Codes below show the five operations:

// number of elements we'll put in our stack
const stack<int>::size_type stk_size = 10;
stack<int> intStack;  // empty stack
 
// fill up the stack
int ix = 0;
while(intStack.size() != stk_size)
    // use postfix increment; want to push old value onto intStack
    intStack.push_back(ix++);       // intStack holds 0...9 inclusive
     
int error_cnt = 0;
while(intStack.empty() == false)
{
    int value = intStack.top();
     
    // read the top element of the stack
    if(value != --ix)
    {
        cerr << "oops! expected " << ix
             << " received " << value << endl;
             ++error_cnt;
    }
    intStack.pop();     // pop the top element, and repeat
}
 
cout << "Our program ran with "
     << error_cnt << " errors!" << endl;