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Specifies variables with the POINTER attribute. SyntaxThe syntax of a type declaration statement with the POINTER
attribute is: type, attrib-list :: dummy-argument-name-list |
- type
is a valid type specification (INTEGER,
REAL, LOGICAL,
CHARACTER, TYPE
( name),
etc.). - attrib-list
is a comma-separated list of attributes including
POINTER and optionally
those attributes compatible with it, namely: - dummy-argument-name-list
is a comma-separated list of dummy-argument-names.
The syntax of the POINTER
statement is: POINTER [::] object-name [(deferred-shape-spec-list)] |
[,object-name [(deferred-shape-spec-list)]]... |
- object-name
is a data object or function result. - deferred-shape-spec-list
is a comma-separated list of colons.
DescriptionA POINTER
attribute or statement specifies that the named variables may be
pointers to some target object. Pointers provide a capability for
creating dynamic objects, such as dynamic-sized arrays and linked
lists. An object with a pointer attribute initially has no space
reserved for its target. A pointer is assigned space for its target
when an ALLOCATE
statement is executed or when it is assigned to point to a target
using a pointer assignment statement. ExamplesIn the first example, two array pointers are declared and
used. ! Extents are not specified; they are determined during execution
REAL, POINTER :: weight (:,:,:)
REAL, POINTER :: w_reg (:,:,:)
READ *, i, j, k
ALLOCATE (weight (i, j, k)) ! create weight
! w_reg is an alias for an array section
w_reg => weight (3:i-2, 3:j-2, 3:k-2)
avg_w = sum (w_reg) / ((i-4) * (j-4) * (k-4))
DEALLOCATE (weight) ! weight no longer needed |
The next example illustrates the use of pointers in a list-processing
application. TYPE link
REAL value
TYPE (link), POINTER :: next
END TYPE link
TYPE(link), POINTER :: list, save_list
NULLIFY (list) ! Initialize list
DO
READ (*, *, IOSTAT = no_more) value
IF (no_more /= 0) EXIT
save_list => list
ALLOCATE (list) ! Add link to head of list
list % value = value
list % next => save_list
END DO
! Linked list removed when no longer needed
DO
IF (.NOT.ASSOCIATED (list) ) EXIT
save_list => list % next
DEALLOCATE (list)
list => save_list
END DO |
Related statementsALLOCATE,
DEALLOCATE, NULLIFY
and TARGET Related conceptsFor related information, see the following: |
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