| Lesson 2 | Design of the Stack |
| Objective | Examine the design of a dynamically sized stack. |
Design of the Stack in C++
A constructor can also be used to allocate space from free store.
To illustrate this, let us modify the ch_stack type we looked at in a previous module so that its maximum length is initialized by a constructor.
//ch_stack implementation with constructor.
class ch_stack {
public:
//the public interface for the ADT ch_stack
explicit ch_stack(int size):
max_len(size), top(EMPTY) {
assert(size > 0);
s = new char[size];
assert(s);
}
void reset() { top = EMPTY; }
void push(char c) {
assert(top != FULL);
top++;
s[top] = c;
}
char pop() {
assert(top!= EMPTY);
return s[top--];
}
char top_of() {
assert(top!= EMPTY);
return s[top];
}
bool empty() const
{ return (top == EMPTY); }
bool full() const
{ return (top == max_len - 1); }
private:
enum { EMPTY = -1 };
char* s; //changed from s[max_len]
int max_len;
int top;
};
The design of the class ch_stack includes hidden implementation detail.
Data members are placed in the private access region of class ch_stack. Remember that generally data is part of an implementation choice. It should be accessed through public member functions.
Accessor and mutator functions in C++
Member functions that are public are called accessor functions when they do not change the object's data.
Accessor functions should be declared const. In ch_stack, top_of() and empty() are accessor functions.
Some of these functions, such as push() and pop(), are called mutator functions because they do change data in the ch_stack object.
The constructor member functions have the job of creating and initializing ch_stack objects.