Object-oriented Software in Ada 95

Dynamic memory allocation 217
The package body is as follows:
with Unchecked_Deallocation;
pragma Elaborate_All( Unchecked_Deallocation );
package body Class_Stack is
procedure Dispose is
new Unchecked_Deallocation( Node, P_Node );
The procedure Dispose is an instantiation of the generic package Unchecked_Deallocation that
returns space back to the heap. The parameters to the generic package Unchecked_Deallocation are of two
types: firstly, the type of the object to be disposed, and secondly, the access type for this object.
Note: This procedure does little error checking. It is important not to dispose of storage which is still active.
The empty list is represented by the p_head containing the null pointer. The null pointer is used to
indicate that currently the object P_Head does not point to any storage. This can be imagined as Figure 15.4.
P_Head
Figure 15.4 A location containing the null access value or pointer.
When an item (in this case an Integer) has been added to the stack it will look like Figure 15.5.
P_Head
3
Value P_Next
Figure 15.5 A stack containing one element.
To access the component value the . operator is used.
Note:
The compiler will generate the appropriate code to reference value. In this case it will involve a dereferencing
through the pointer held in P_Head.
P_Head.Item = 3;
The function Push creates a new element and chains this into a linked list of elements which hold the items
pushed onto the stack.
The chain of elements after adding 3 and
2 to an instance of an Integer Stack
The chain of elements after pushing 1 on
to an instance of an Integer Stack
P_Head
P_Head
1
2
2
3
3
© M A Smith - May not be reproduced without permission