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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.


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