## 2.3.2 Fixed and Tab Source Forms

In Fortran 95, fixed source form is identified as obsolescent.

In fixed and tab source forms, there are restrictions on where a statement can appear within a line.

By default, a statement can extend to character position 72. In this case, any text following position 72 is ignored and no warning message is printed. You can specify a compiler option to extend source lines to character position 132.

Except in a character context, blanks are not significant and can be used freely throughout the program for maximum legibility.

Some Fortran compilers use blanks to pad short source lines out to 72 characters. By default, Compaq Fortran does not. If portability is a concern, you can use the concatenation operator to prevent source lines from being padded by other Fortran compilers (see the example in "Continuation Indicator" below) or you can force short source lines to be padded by using a compiler option.

Comment Indicator

In fixed and tab source forms, the exclamation point character (!) indicates a comment if it is within a source line. (It must not appear in column 6 of a fixed form line; that column is reserved for a continuation indicator.)

The letter C (or c), an asterisk (*), or an exclamation point (!) indicates a comment line when it appears in column 1 of a source line.

Continuation Indicator

In fixed and tab source forms, a continuation line is indicated by one of the following:

- For fixed form: Any character (except a zero or blank) in column 6 of a source line
- For tab form: Any digit (except zero) after the first tab

The compiler considers the characters following the continuation indicator to be part of the previous line. Although Fortran 95/90 permits up to 19 continuation lines in a fixed-form program, Compaq Fortran allows up to 511 continuation lines.

If a zero or blank is used as a continuation indicator, the compiler considers the line to be an initial line of a Fortran statement.

The statement label field of a continuation line must be blank (except in the case of a debugging statement).

When long character or Hollerith constants are continued across lines, portability problems can occur. Use the concatenation operator to avoid such problems. For example:

          PRINT *, 'This is a very long character constant '//
         +         'which is safely continued across lines'

Use this same method when initializing data with long character or Hollerith constants. For example:

          CHARACTER*(*) LONG_CONST
          PARAMETER (LONG_CONST = 'This is a very long '//
         + 'character constant which is safely continued '//
         + 'across lines')
          CHARACTER*100 LONG_VAL
          DATA LONG_VAL /LONG_CONST/

Hollerith constants must be converted to character constants before using the concatenation method of line continuation.

Debugging Statement Indicator

In fixed and tab source forms, the statement label field can contain a statement label, a comment indicator, or a debugging statement indicator.

The letter D indicates a debugging statement when it appears in column 1 of a source line. The initial line of the debugging statement can contain a statement label in the remaining columns of the statement label field.

If a debugging statement is continued onto more than one line, every continuation line must begin with a D and a continuation indicator.

By default, the compiler treats debugging statements as comments. However, you can specify a compiler option to force the compiler to treat debugging statements as source text to be compiled.

For More Information:

- On the general rules for all source forms, see Section 2.3.
- On statement separators (;) in all forms, see Section 2.3.
- On compiler options, see your user manual or programmer's guide.
- On the OPTIONS statement, see Section 14.2.
- On statement labels, see Section 2.3.
- On obsolescent features in Fortran 95, see Appendix A.

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