Defines a
named constant.
Syntax
A type declaration statement with the PARAMETER attribute is:
type, attrib-list :: cname1 = cexpr1[, cname2 = cexpr2]... |
- type
is a valid type specification (INTEGER, REAL, LOGICAL, CHARACTER, TYPE (name), etc.).
- attrib-list
is a comma-separated list of attributes including PARAMETER and optionally those attributes compatible with
it, namely:
Table 10-42 Title not available (PARAMETER (statement and attribute))
DIMENSION | PUBLIC | |
PRIVATE | SAVE | |
Specifying
the SAVE attribute in a PARAMETER statement has no effect.
- cname
is the name that will represent the constant.
- cexpr
is an initialization
expression that evaluates to the constant represented by cname. In the case of an array constant, cexpr must be an array constructor. In the case of a derived
type constant, cexpr must be a structure constructor.
The syntax of the PARAMETER statement is:
PARAMETER (cname1 = cexpr1 [, cname2 = cexpr2]...) |
Description
The PARAMETER statement associates a symbolic name with a constant.
A symbolic name defined in a PARAMETER statement is known as a named constant.
A named constant must not become defined more than once in a program
unit. Once defined, it can be used only as a named constant. This
means that a named constant cannot be assigned a value like a variable.
When the PARAMETER attribute is used, the value of the named constant
must be provided by the initialization part of the statement in
which the PARAMETER attribute appears.
The type of a named constant is determined by the implicit
typing rules, unless its type is specified by a type declaration
statement prior to its first appearance in a PARAMETER statement or by a type declaration statement that
includes PARAMETER as one of its attributes. If a PARAMETER statement declares and implicitly types a named
constant, the named constant may appear in a subsequent type declaration
or IMPLICIT statement, but only to confirm the type of the
named constant.
When the type of the symbolic name and the constant do not
agree, the value of the named constant is assigned in accordance
with assignment statement type-conversion rules, as given in Table 4-5 “Conversion of variable=expression”.
The following
rules apply to type agreement between the constant and the symbolic
name:
If cname is of numeric type, cexpr must be an arithmetic constant expression.
If cname is of type character, the corresponding cexpr must be a character constant expression.
If cname is of type logical, the corresponding cexpr may be either an arithmetic or logical constant expression.
Any symbolic name of a constant that appears in cexpr must have been defined previously in the same or
a different PARAMETER statement in the same program unit. For example,
the expression in the second PARAMETER statement below is built from the expression in
the first PARAMETER statement, and is legal:
PARAMETER (limit = 1000)
PARAMETER (limit_plus_1 = limit + 1) |
The logical
operators (.EQ., .NE., .LT., .LE., .GT., and .GE.), as well as the following intrinsic functions,
can appear in the PARAMETER statement:
Table 10-43 Title not available (PARAMETER (statement and attribute))
ABS | IAND | IXOR | MAX |
CHAR | ICHAR | LEN | MIN |
CMPLX | IEOR | LGE | MOD |
CONJB | IMAG | LGT | NINT |
DIM | IOR | LLE | NOT |
DPROD | ISHFT | LLT | |
If these intrinsic functions are used in a PARAMETER statement, their arguments must be constants.
If the named
constant is of type character and its length is not specified, the
length must be specified in a type declaration statement or IMPLICIT statement prior to the first appearance of the
named constant. Its type and/or length must not be changed by subsequent
statements, including IMPLICIT statements. If a symbolic name of type CHARACTER*(*) is defined in a PARAMETER statement, its length becomes the length of the
expression assigned to it.
If the named constant is an array, the bounds must be explicit
and determined by an initialization expression.
Once such
a symbolic name is defined, that name can appear in any subsequent
statement of the defining program unit as a constant in an expression
or DATA statement.
Examples
! PARAMETER used in a type declaration statement as an attribute
REAL, DIMENSION(4), PARAMETER :: const = &
(/1.2, 1.45, 0.9, 24.3/)
INTEGER year
! PARAMETER used as a statement
PARAMETER year = 1996
! Type declaration statement declaring a derived-type constant
TYPE (postal_info), PARAMETER :: package = &
postal_info (9.5, (/10.0, 5.5, 2.25/) ) |
Related concepts
For information about the type declaration statement, see “Type
declaration for intrinsic types”.
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