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Developer Guide and Reference

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ID 767251

Date 10/31/2024

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Free Source Form

In free source form, statements are not limited to specific positions on a source line. In Standard Fortran, a free form source line can contain from 0 to 10,000 characters.

Blank characters are significant in free source form. The following are rules for blank characters:

Blank characters must not appear in lexical tokens, except within a character context. For example, there can be no blanks between the exponentiation operator **. Blank characters can be used freely between lexical tokens to improve legibility. Intel® Fortran allows the line to be of any length.
Blank characters must be used to separate names, constants, or labels from adjacent keywords, names, constants, or labels. For example, consider the following statements:
```
  INTEGER NUM
  GO TO 40
  20 DO K=1,8
```
The blanks are required after INTEGER, TO, 20, and DO.

Some adjacent keywords must have one or more blank characters between them. Others do not require any; for example, BLOCK DATA can also be spelled BLOCKDATA. The following list shows which keywords have optional or required blanks:

Optional Blanks	Required Blanks
BLOCK DATA	ABSTRACT INTERFACE
DOUBLE COMPLEX	CASE DEFAULT
DOUBLE PRECISION	CHANGE TEAM
ELSE IF	CLASS DEFAULT
ELSE WHERE	CLASS IS
END ASSOCIATE	DO CONCURRENT
END BLOCK	DO WHILE
END BLOCK DATA	ERROR STOP
END CRITICAL	EVENT POST
END DO	EVENT WAIT
END ENUM	FAIL IMAGE
END FILE	FORM TEAM
END FORALL	IMPLICIT `type-specifier`
END FUNCTION	IMPLICIT NONE
END IF	INTERFACE ASSIGNMENT
END INTERFACE	INTERFACE OPERATOR
END MODULE	MODULE PROCEDURE
END PROCEDURE	`prefix`^¹ [`prefix` …] FUNCTION
END PROGRAM	`prefix`^¹ [`prefix` …] `type-specifier` [`prefix`...] FUNCTION
END SELECT	`prefix`^¹ [`prefix` …] SUBROUTINE
END SUBMODULE	RANK DEFAULT
END SUBROUTINE	SYNC ALL
END TEAM	SYNC IMAGES
END TYPE	SYNC MEMORY
END WHERE	SYNC TEAM
GO TO	`type-specifier` FUNCTION
IN OUT	`type-specifier` `prefix`^¹ [`prefix` …] FUNCTION
SELECT CASE
SELECT RANK
SELECT TYPE
¹`prefix` is ELEMENTAL or IMPURE or MODULE or NON_RECURSIVE or PURE or RECURSIVE. No `prefix` can be specified more than once. You cannot specify both IMPURE and PURE. You cannot specify both NON_RECURSIVE and RECURSIVE.

For information on statement separators (;) in all forms, see Source Forms.

Comment Indicator

In free source form, the exclamation point character (!) indicates a comment if it is within a source line, or a comment line if it is the first character in a source line.

Continuation Indicator

In free source form, the ampersand character (&) indicates a continuation line (unless it appears in a Hollerith or character constant, or within a comment). The continuation line is the first noncomment line following the ampersand. A comment line cannot be continued, but a comment can appear in a continuation line.

A line cannot contain a single "&" as the only non-blank character or as the only non-blank character before an "!" that begins a comment. The Fortran Standard limits a statement to a total of 1,000,000 characters, but it does not limit the number of continuation lines.

The following shows a continued statement:

  TCOSH(Y) = EXP(Y) + &    ! The initial statement line
    EXP(-Y)                ! A continuation line

If the first nonblank character on the next noncomment line is an ampersand, the statement continues at the character following the ampersand. For example, the preceding example can be written as follows:

  TCOSH(Y) = EXP(Y) + &
   & EXP(-Y)

If a lexical token must be continued, the first nonblank character on the next noncomment line must be an ampersand followed immediately by the rest of the token. For example:

    TCOSH(Y) = EXP(Y) + EX&
 &P(-Y)

If you continue a character constant, an ampersand must be the first non-blank character of the continued line; the statement continues with the next character following the ampersand. For example:

  ADVERTISER = "Davis, O'Brien, Chalmers & Peter&
          &son"
  ARCHITECT  = "O'Connor, Emerson, and Dickinson&
        &  Associates"

If the ampersand is omitted on the continued line, the statement continues with the first non-blank character in the continued line. So, in the preceding example, the whitespace before "Associates" would be ignored.

The ampersand cannot be the only nonblank character in a line, or the only nonblank character before a comment; an ampersand in a comment is ignored.

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