Stack Adaptor

The stack type is defined in the stack header. The operations provided by a stack are listed in Table 9.18. The following program illustrates the use of stack:

stack<int> intStack;  // empty stack
// fill up the stack
for (size_t ix = 0; ix != 10; ++ix)
    intStack.push(ix);   // intStackholds 0 ... 9 inclusive
while (!intStack.empty()) {    // while there are still values in intStack
    int value = intStack.top();
    // code that uses value
    intStack.pop(); // pop the top element, and repeat
}

Table 9.18. Stack Operations in Addition to Those in Table 9.17

The declaration

stack<int> intStack;  // empty stack

defines intStack to be an empty stack that holds integer elements. The for loop adds ten elements, initializing each to the next integer in sequence starting from zero. The while loop iterates through the entire stack, examining the top value and popping it from the stack until the stack is empty.

Each container adaptor defines its own operations in terms of operations provided by the underlying container type. We can use only the adaptor operations and cannot use the operations of the underlying container type. For example,

intStack.push(ix);   // intStackholds 0 ... 9 inclusive

calls push_back on the deque object on which intStack is based. Although stack is implemented by using a deque, we have no direct access to the deque operations. We cannot call push_back on a stack; instead, we must use the stack operation named push.