4.2 Options Controlling Fortran Dialect

The following options control the dialect of Fortran that the compiler accepts:

-ffree-form

-ffixed-form

Specify the layout used by the source file. The free form layout was introduced in Fortran 90. Fixed form was traditionally used in older Fortran programs.

-fd-lines-as-code

-fd-lines-as-comment

Enables special treating for lines with `d' or `D' in fixed form sources. If the -fd-lines-as-code option is given they are treated as if the first column contained a blank. If the -fd-lines-as-comments option is given, they are treated as comment lines.

-fdefault-double-8

Set the "DOUBLE PRECISION" type to an 8 byte wide.

-fdefault-integer-8

Set the default integer and logical types to an 8 byte wide type. Do nothing if this is already the default.

-fdefault-real-8

Set the default real type to an 8 byte wide type. Do nothing if this is already the default.

-fdollar-ok

Allow `$' as a valid character in a symbol name.

-fno-backslash

Compile switch to change the interpretation of a backslash from “C”-style escape characters to a single backslash character.

-ffixed-line-length-n

Set column after which characters are ignored in typical fixed-form lines in the source file, and through which spaces are assumed (as if padded to that length) after the ends of short fixed-form lines.

Popular values for n include 72 (the standard and the default), 80 (card image), and 132 (corresponds to “extended-source” options in some popular compilers). n may be `none', meaning that the entire line is meaningful and that continued character constants never have implicit spaces appended to them to fill out the line. -ffixed-line-length-0 means the same thing as -ffixed-line-length-none.

-ffree-line-length-n

Set column after which characters are ignored in typical free-form lines in the source file. For free-form, the default value is 132. n may be `none', meaning that the entire line is meaningful. -ffree-line-length-0 means the same thing as -ffree-line-length-none.

-fmax-identifier-length=n

Specify the maximum allowed identifier length. Typical values are 31 (Fortran 95) and 63 (Fortran 200x).

-fimplicit-none

Specify that no implicit typing is allowed, unless overridden by explicit `IMPLICIT' statements. This is the equivalent of adding `implicit none' to the start of every procedure.

-fcray-pointer

Enables the Cray pointer extension, which provides a C-like pointer.

-frange-check

Enable range checking on results of simplification of constant expressions during compilation. For example, by default, gfortran will give an overflow error at compile time when simplifying a = EXP(1000). With `-fno-range-check', no error will be given and the variable a will be assigned the value +Infinity.

-std=std

Conform to the specified standard. Allowed values for std are `gnu', `f95', `f2003' and `legacy'.