CS1001%20Lecture%2026

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CS1001 Lecture 26

• Static vs Dynamic Data Structures
• Array vs Link List
• Pointers
• Link List Operations
• Example

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Static vs Dynamic

• Static Data Structure -- structures whose sizes
  are fixed once memory is allocated, e.g., arrays
• type, DIMENSION (lu) list_of _array_names
• type, DIMENSION () , ALLOCATABLE list
• ALLOCATE (list, STAT status_variable)
• DEALLOCATE (list, STAT status_variable)
• Dynamic Data Structure -- expands and contracts
  as needed during execution
• collection of elements called nodes
• e.g., Link list

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Arrays

• PROs
• Used for list of data that can be naturally
  organized into tables
• Easy and fast to access each element by indices
• Easy and fast to operate on corresponding data
  points
• CONs
• Fixed size
• Hard to shift elements

1, 3, 5, 8,10,, 80, to insert 2 1, 2, 3, 5,
8, 10, , 80, ...
1, 2, 3, 5, 8, 10,, 80, to delete 3 1, 2, 5,
8, 10, , 80, ...
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Link List

• Link list -- collection of elements called nodes
  and each node consists of data and link (or
  pointer)

data
data
data
list
Brown ptr
CMU ptr
WPI null
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Adding to the linked list
Data next
data next
data next
list
Brown
CMU
WPI null
data
new
Prev_ptr
RICE
data next
data next
data next
list
Brown
CMU
WPI null
data
new
Prev_ptr
RICE
data next
data next
data next
list
Brown
CMU
WPI null
data
new
Prev_ptr
RICE
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Delete a node from a linked list
data next
data next
data next
list
Brown
CMU
WPI null
data
Prev_ptr
To_delete
RICE
data next
data next
data next
list
Brown
CMU
WPI null
data
To_delete
Prev_ptr
RICE
data next
data next
null
list
Brown
WPI null
To_delete
data
Prev_ptr
RICE
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Linked List Elements

• Pointer to the List
• Node -- defined as a derived type
• e.g., TYPE School_node
• CHARACTER(8) Name
• TYPE (School_node) POINTER next
• END TYPE School_node
• e.g., TYPE School
• CHARACTER(8) Name
• REAL Cost
• END TYPE School
• TYPE School_node1
• TYPE School data
• TYPE (School_node1) POINTER next
• END TYPE School_node1

School_node
Name next
School_node1
data next
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Pointers

• Declaration
• Type, attribute_list, POINTER pointer_variable
• e.g., CHARACTER(8), POINTER StringPtr
• TYPE (School_node1), POINTER NextPtr
• ALLOCATE
• Used to acquire memory locations to associate
  with the pointer variable during execution
• e.g., ALLOCATE(StringPtr)
• ALLOCATE (NextPtr)

Memory for data of type School_node1
Name -- Character(8) Cost -- Real Next -- pointer
to type School_node1
StringPtr
NextPtr
Character(8)
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Pointer

• Pointer variables
• undefined
• initially undefined
• associated -- when a pointer points to a target
• intrinsic function ASSOCIATED to test whether a
  pointer variable is associated with a target.
  E.g., ASSOCIATED (pointer) returns .TRUE. if
  association exists, returns .FALSE. otherwise.
• null or disassociated
• NULLIFY (list_of_pointers) change pointer
  variables to null
• the association between that pointer and the
  target memory location is broken
• DEALLOCATE statement is used to free the target
  memory

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Pointer Assignment

• Form pointer1 gt pointer2
• if pointer1 and pointer2 have the same type

Pointer1 Pointer2
Need another pointer ?
Pointer1 gt Pointer2
Pointer1 Pointer2
ASSOCIATED ( Pointer1, Pointer2) .TRUE. If
pointer1 and pointer2 point to the same
target. .FALSE. Otherwise.
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Pointers in expressions

• CHARACTER (8), POINTER School
• TYPE School_node
• CHARACTER(8) Name
• TYPE (School_node) POINTER next
• END TYPE School_node
• TYPE (School_node), POINTER list
• ALLOCATE (School)
• ALLOCATE (list)
• School Stanford
• Print , School

School
CHARACTER(8)
list
CHARACTER(8) Pointer to School_node
School
Stanford
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Pointers in expressions

• CHARACTER (8), POINTER School1, School2
• ALLOCATE (School1)
• ALLOCATE (School2)
• School1 Stanford
• School2 Cornell
• School1 School2
• School1 gt School2

Stanford
School1
Cornell
School2
Cornell
School1
Cornell
School2
Stanford
School1
Cornell
School2
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Constructing a Linked List

• TYPE School_node
• CHARACTER(8) Name
• TYPE (School_node) POINTER next
• END TYPE School_node
• TYPE (School_node), POINTER list, temp
• ALLOCATE (temp)
• tempName Stanford
• NULLIFY(tempnext)
• list gt temp
• ALLOCATE(temp)
• tempName WPI
• NULLIFY(tempnext)
• listnext gt temp

CHARACTER(8) Pointer to School_node
Stanford Null
temp
list
list
Stanford Null
WPI Null
temp
temp
list
Stanford
WPI Null
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Traversing a linked list
WPI
Cornell Null
list
Stanford
Curr_ptr
Curr_ptr gt list Curr_ptr gt Curr_ptrnext Curr_pt
r gt Curr_ptrnext Curr_ptr gt Curr_ptrnext
Curr_ptr
Curr_ptr
Curr_ptr is null -- end of list
Curr_ptr gt list DO IF (.NOT. ASSOCIATED
(Curr_ptr) EXIT PRINT , Curr_ptrname
Curr_ptr gt Curr_ptrnext END DO
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Example

• Get a list of TCP/IP address from a file
• Use linked list to keep track of how many times
  the addresses was used
• traverse the list and display each TCP/IP
  address and its counts