[Chapter 5] 5.24 PLVstk: Stack Manager

5.24 PLVstk: Stack Manager

The PLVstk (PL/Vision STacK manager) package is a generic manager for both first-in-first-out ( FIFO ) and last-in-last-out ( LIFO ) stacks; it is built on PLVlst. See the companion disk for details.

5.24.1 Package constants

defstk CONSTANT VARCHAR2(5) := 'stack';: The name of the default stack.
lifo CONSTANT VARCHAR2(4) := 'LIFO';: Indicates that you are working with a last-in-first-out stack. Used in calls to pop .
fifo CONSTANT VARCHAR2(4) := 'FIFO';: Indicates that you are working with a first-in-first-out stack. Used in calls to pop .

5.24.2 Creating and destroying stacks

PROCEDURE make
(stack_in IN VARCHAR2 := defstk,
overwrite_in IN BOOLEAN := TRUE);: Allocates storage for a stack of up to 1,000 items with the specified name. By default, if the stack already exists it will be reinitialized to an empty stack.
PROCEDURE destroy (stack_in IN VARCHAR2 := defstk);: Releases all memory associated with this stack.

5.24.3 Modifying stack contents

PROCEDURE push
(item_in IN VARCHAR2, stack_in IN VARCHAR2 := defstk);: Pushes an item onto the specified stack.
PROCEDURE pop
(value_out IN OUT VARCHAR2,
stack_in IN VARCHAR2 := defstk,
stack_type_in IN VARCHAR2 := lifo);: Pops an item off the top ( LIFO ) or bottom ( FIFO ) of the stack.

5.24.4 Analyzing stack contents

FUNCTION nitems (stack_in IN VARCHAR2 := defstk)
RETURN INTEGER;: Returns the number of items currently in the stack.
FUNCTION itemin (stack_in IN VARCHAR2, item_in IN VARCHAR2)
RETURN BOOLEAN;: Returns TRUE if the specified item is found in the stack.

5.24.5 Tracing Stack Activity

PROCEDURE show
(stack_in IN VARCHAR2 := defstk,
show_contents_in IN BOOLEAN := FALSE);: Requests that pre-action status of stack be displayed for the specified stack (or all).
PROCEDURE noshow;: Turns off display of pre-action status.
FUNCTION showing RETURN BOOLEAN;: Returns TRUE if showing pre-action status.
PROCEDURE verify
(stack_in IN VARCHAR2 := defstk,
show_contents_in IN BOOLEAN := FALSE);: Requests that post-action status of stack be displayed for the specified stack (or all).
PROCEDURE noverify;: Turns off display of post-action status.
FUNCTION verifying RETURN BOOLEAN;: Returns TRUE if showing post-action status.


5.23 PLVrb: Rollback Processing		5.25 PLVtab: Table Interface