Declarations for Character Types

A CHARACTER type specifier can be immediately followed by the length of the character object or function. It takes one of the following forms:

Keyword Forms

CHARACTER [([LEN=]len)]

CHARACTER [([LEN=]len [, [KIND=]n])]

CHARACTER [(KIND=n [, LEN=len])]

Nonkeyword Form

CHARACTER*len[,]

len

Is a length type parameter. It can have one of the following values:

A scalar integer expression
*
:

The following rules also apply:

In keyword forms

The len is a specification expression, an asterisk (*), or a colon (:). If no length is specified, the default length is 1.

If the length evaluates to a negative value, the length of the character entity is zero.
In nonkeyword form

The len is a specification expression or an asterisk enclosed in parentheses, or a scalar integer literal constant (with no kind parameter). The comma is permitted only if no double colon (::) appears in the type declaration statement.

This form can also (optionally) be specified following the name of the data object or function (v*len). In this case, the length specified overrides any length following the CHARACTER type specifier.

The largest valid value for len in both forms is 2**31-1 on IA-32 architecture; 2**63-1 on Intel® 64 architecture. Negative values are treated as zero.

n

Is a scalar integer constant expression specifying a valid kind parameter. Currently the only kind available is 1.

Description

An automatic object can appear in a character declaration. The object cannot be a dummy argument, and its length must be declared with a specification expression that is not a constant expression.

The length specified for a character-valued statement function or statement function dummy argument of type character must be an integer constant expression.

When an asterisk length specification *(*) is used for a function name or dummy argument, it assumes the length of the corresponding function reference or actual argument. Similarly, when an asterisk length specification is used for a named constant, the name assumes the length of the actual constant it represents. For example, STRING assumes a 9-byte length in the following statements:

  CHARACTER*(*) STRING
  PARAMETER (STRING = 'VALUE IS:')

A function name must not be declared with a * length unless it is of type CHARACTER and is the name of the result of an external function or the name of a dummy function.

A function name declared with a * length must not be an array, a pointer, recursive, elemental, or pure.

If the CHARACTER type declaration statement specifies a colon (:) length, the length type parameter is a deferred type parameter. An entity or component with a deferred type parameter must specify the ALLOCATABLE or POINTER attribute. A deferred type parameter is a length type parameter whose value can change during execution of the program.

The nonkeyword form is considered obsolescent in the Fortran standard.

Examples

In the following example, the character string last_name is given a length of 20:

  CHARACTER (LEN=20) last_name

In the following example, stri is given a length of 12, while the other two variables retain a length of 8.

  CHARACTER *8 strg, strh, stri*12

In the following example, a dummy argument strh will assume the length of the associated actual argument, while the other two variables retain a length of 8:

  CHARACTER *8 strg, strh(*), stri

The following examples show ways to specify strings of known length:

  CHARACTER*32 string1
  CHARACTER string2*32

The following examples show ways to specify strings of unknown length:

  CHARACTER string3*(*)
  CHARACTER*(*) string4

The following example declares an array NAMES containing 100 32-character elements, an array SOCSEC containing 100 9-character elements, and a variable NAMETY that is 10 characters long and has an initial value of 'ABCDEFGHIJ'.

  CHARACTER*32 NAMES(100),SOCSEC(100)*9,NAMETY*10 /'ABCDEFGHIJ'/

The following example includes a CHARACTER statement declaring two 8-character variables, LAST and FIRST.

  INTEGER, PARAMETER :: LENGTH=4
  CHARACTER*(4+LENGTH) LAST, FIRST

The following example shows a CHARACTER statement declaring an array LETTER containing 26 one-character elements. It also declares a dummy argument BUBBLE that has a passed length defined by the calling program.

  CHARACTER LETTER(26), BUBBLE*(*)

In the following example, NAME2 is an automatic object:

  SUBROUTINE AUTO_NAME(NAME1)
    CHARACTER(LEN = *) NAME1
    CHARACTER(LEN = LEN(NAME1)) NAME2

The following example shows the handling of a deferred-length CHARACTER variables:


CHARACTER(:), ALLOCATABLE :: namea
namea = 'XYZ'                   ! Allocates namea as length 3 with value 'XYZ'
DEALLOCATE (namea)
ALLOCATE (CHARACTER(10)::namea) ! Allocates namea as length 10, no value
namea = 'ABCDEF'                ! Reallocates namea to length 6 with value 'ABCDEF'

Declarations for Character Types

Description

Examples

See Also