Type Declarations

Statement: Explicitly specifies the properties of data objects or functions.

Syntax

A type declaration statement has the general form:

type [ [, att ] ... :: ] v [/c-list/] [, v [/c-list/] ] ...

type
Is one of the following data type specifiers:

BYTE
INTEGER [([KIND=]k)]
REAL [([KIND=]k)]
DOUBLE PRECISION
COMPLEX [([KIND=]k)]
DOUBLE COMPLEX
CHARACTER [([KIND=]k)]
LOGICAL [([KIND=]k)]
TYPE (derived-type-name)

In the optional kind selector "([KIND=]k)", k is the kind parameter. It must be an acceptable kind parameter for that data type. If the kind selector is not present, entities declared are of default type.

Kind parameters for intrinsic numeric and logical data types can also be specified using the *n format, where n is the length (in bytes) of the entity; for example, INTEGER*4.

See each data type for further information on that type.

att
Is one of the following attribute specifiers:

ALLOCATABLE	INTRINSIC	SAVE
ASYNCHRONOUS	OPTIONAL	STATIC
AUTOMATIC	PARAMETER	TARGET
BIND	POINTER	VALUE
DIMENSION	PRIVATE ¹	VOLATILE
EXTERNAL	PROTECTED
INTENT	PUBLIC ¹
¹ These are access specifiers.

You can also declare any attribute separately as a statement.

v
Is the name of a data object or function. It can optionally be followed by:

An array specification, if the object is an array.
In a function declaration, an array must be a deferred-shape array if it has the POINTER attribute; otherwise, it must be an explicit-shape array.
A character length, if the object is of type character.
An initialization expression preceded by an = or, for pointer objects, => NULL( ).

A function name must be the name of an intrinsic function, external function, function dummy procedure, or statement function.

c-list
Is a list of constants, as in a DATA statement. If v is the name of a constant or an initialization expression, the c-list cannot be present.

The c-list cannot specify more than one value unless it initializes an array. When initializing an array, the c-list must contain a value for every element in the array.

Description

Type declaration statements must precede all executable statements.

In most cases, a type declaration statement overrides (or confirms) the implicit type of an entity. However, a variable that appears in a DATA statement and is typed implicitly can appear in a subsequent type declaration only if that declaration confirms the implicit typing.

The double colon separator (::) is required only if the declaration contains an attribute specifier or initialization; otherwise it is optional.

If att appears, c-list cannot be specified; for example:

  INTEGER I /2/              ! Valid
  INTEGER, SAVE :: I /2/     ! Invalid

The same attribute must not appear more than once in a given type declaration statement, and an entity cannot be given the same attribute more than once in a scoping unit.

If the PARAMETER attribute is specified, the declaration must contain an initialization expression.

If => NULL( ) is specified for a pointer, its initial association status is disassociated.

A variable (or variable subobject) can only be initialized once in an executable program.

The INTENT, VALUE, and OPTIONAL attributes can be specified only for dummy arguments.

The VALUE attribute must not be specified for a dummy procedure.

If a declaration contains an initialization expression, but no PARAMETER attribute is specified, the object is a variable whose value is initially defined. The object becomes defined with the value determined from the initialization expression according to the rules of intrinsic assignment.

The presence of initialization implies that the name of the object is saved, except for objects in named common blocks or objects with the PARAMETER attribute.

The following objects cannot be initialized in a type declaration statement:

A dummy argument
A function result
An object in a named common block (unless the type declaration is in a block data program unit)
An object in blank common
An allocatable array
An external name
An intrinsic name
An automatic object
An object that has the AUTOMATIC attribute

An object can have more than one attribute. The following table lists the compatible attributes:

Compatible Attributes

Attribute	Compatible with:
ALLOCATABLE	AUTOMATIC, ASYNCHRONOUS, DIMENSION ¹, PRIVATE, PROTECTED, PUBLIC, SAVE, STATIC, TARGET, VOLATILE
ASYNCHRONOUS	ALLOCATABLE, AUTOMATIC, BIND, DIMENSION, INTENT, OPTIONAL, POINTER, PROTECTED, PUBLIC, SAVE, STATIC, TARGET, VOLATILE
AUTOMATIC	ALLOCATABLE, ASYNCHRONOUS, BIND, DIMENSION, POINTER, PROTECTED, TARGET, VOLATILE
BIND	ASYNCHRONOUS, AUTOMATIC, DIMENSION, EXTERNAL, PRIVATE, PROTECTED, PUBLIC, SAVE, STATIC, TARGET, VOLATILE
DIMENSION	ALLOCATABLE, ASYNCHRONOUS, AUTOMATIC, BIND, INTENT, OPTIONAL, PARAMETER, POINTER, PRIVATE, PROTECTED, PUBLIC, SAVE, STATIC, TARGET, VOLATILE
EXTERNAL	BIND, OPTIONAL, PRIVATE, PUBLIC
INTENT	ASYNCHRONOUS, DIMENSION, OPTIONAL, TARGET, VOLATILE
INTRINSIC	PRIVATE, PUBLIC
OPTIONAL	ASYNCHRONOUS, DIMENSION, EXTERNAL, INTENT, POINTER, TARGET, VOLATILE
PARAMETER	DIMENSION, PRIVATE, PUBLIC
POINTER	ASYNCHRONOUS, AUTOMATIC, DIMENSION ¹, OPTIONAL, PRIVATE, PROTECTED, PUBLIC, SAVE, STATIC, VOLATILE
PRIVATE	ASYNCHRONOUS, ALLOCATABLE, BIND, DIMENSION, EXTERNAL, INTRINSIC, PARAMETER, POINTER, PROTECTED, SAVE, STATIC, TARGET, VOLATILE
PROTECTED	ALLOCATABLE, ASYNCHRONOUS, BIND, DIMENSION, POINTER, PRIVATE, PUBLIC, SAVE, TARGET, VOLATILE
PUBLIC	ASYNCHRONOUS, ALLOCATABLE, BIND, DIMENSION, EXTERNAL, INTRINSIC, PARAMETER, POINTER, PROTECTED, SAVE, STATIC, TARGET, VOLATILE
SAVE	ALLOCATABLE, ASYNCHRONOUS, BIND, DIMENSION, POINTER, PRIVATE, PROTECTED, PUBLIC, STATIC, TARGET, VOLATILE
STATIC	ALLOCATABLE, ASYNCHRONOUS, BIND, DIMENSION, POINTER, PRIVATE, PROTECTED, PUBLIC, SAVE, TARGET, VOLATILE
TARGET	ALLOCATABLE, ASYNCHRONOUS, AUTOMATIC, BIND, DIMENSION, INTENT, OPTIONAL, PRIVATE, PROTECTED, PUBLIC, SAVE, STATIC, VOLATILE
VALUE	ASYNCHRONOUS, INTENT (IN only), OPTIONAL, TARGET
VOLATILE	ASYNCHRONOUS, AUTOMATIC, BIND, DIMENSION, INTENT, OPTIONAL, POINTER, PRIVATE, PROTECTED, PUBLIC, SAVE, STATIC, TARGET
¹ With deferred shape

Examples

The following show valid type declaration statements:

DOUBLE PRECISION B(6)
INTEGER(KIND=2) I
REAL(KIND=4) X, Y
REAL(4) X, Y
LOGICAL, DIMENSION(10,10) :: ARRAY_A, ARRAY_B
INTEGER, PARAMETER :: SMALLEST = SELECTED_REAL_KIND(6, 70)
REAL(KIND (0.0)) M
COMPLEX(KIND=8) :: D
TYPE(EMPLOYEE) :: MANAGER
REAL, INTRINSIC :: COS
CHARACTER(15) PROMPT
CHARACTER*12, SAVE :: HELLO_MSG
INTEGER COUNT, MATRIX(4,4), SUM
LOGICAL*2 SWITCH
REAL :: X = 2.0
TYPE (NUM), POINTER :: FIRST => NULL()

The following shows more examples:

 REAL a (10)
 LOGICAL, DIMENSION (5, 5) :: mask1, mask2
 COMPLEX :: cube_root = (-0.5, 0.867)
 INTEGER, PARAMETER :: short = SELECTED_INT_KIND (4)
 REAL (KIND (0.0D0)) a1
 REAL (KIND = 2) b
 COMPLEX (KIND = KIND (0.0D0)) :: c
 INTEGER (short) k ! Range at least -9999 to 9999
 TYPE (member) :: george