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The Stacks class implements the standard version of a last-in-first-out (LIFO) stack. Three different implementations of stacks are offered by the GNU C++ class library: the VStack, the XPStack, and the SLStack. The VStack is a fixed-size stack, meaning that you must specify an upper bound on the size of the stack when you first create it. The XPStack and the SLStack are both dynamically sized stacks that are implemented in a slightly different way.
Table 27.8 lists the operations that can be performed on the Stacks classes.
| Operator | Description | ||
|---|---|---|---|
| Stack st | Declares st to be a stack | ||
| Stack st(sz) | Declares st to be a stack of size sz | ||
| st.empty() | Returns TRUE if stack is empty | ||
| st.full() | Returns TRUE if stack is full | ||
| st.length() | Returns the number of elements in stack | ||
| st.push(x) | Puts element x onto the top of the stack | ||
| x= st.pop() | Removes and returns the top element from the stack | ||
| st.top() | Returns a pointer to the top element in the stack | ||
| st.del_top() | Deletes the top element from the stack without returning it | ||
| st.clear() | Deletes all elements from stack
| ||
The Queue class implements a standard version of a first-in-first-out (FIFO) queue. Three different kinds of queue are provided by the GNU C++ class library: the VQueue, the XPQueue, and the SLQueue. The VQueue is a fixed-size queue, so you must specify an upper bound on the size of this kind of queue when you first create it. The XPQueue and the SLQueue are both dynamically sized queues, so no upper bound is required. The operations supported by the Queue classes are listed in Table 27.9.
| Operator | Description |
|---|---|
| Queue q | Declares q to be a queue |
| Queue q(sz) | Declares q to be a queue of size sz |
| q.empty() | Returns TRUE if q is empty |
| q.full() | Returns TRUE if q is full |
| q.length() | Returns the number of elements in q |
| q.enq(x) | Adds the x element to q |
| x= q.deq() | Removes and returns an element from q |
| q.front() | Returns a pointer to the front of q |
| q.del_front() | Removes an element from q and does not return the result |
| q.clear | Removes all elements from the queue |
In addition to the normal kind of queue that is discussed in this section, the GNU C++ class library also supports double-ended queues and priority queues. Both of these types of queues have similar behavior to the regular queue. The double-ended queue adds operators for returning a pointer to the rear of the queue and deleting elements from the rear of the queue. The priority queues are arranged so that a user has fast access to the least element in the queue. They support additional operators that allow for searching for elements in the queue.
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