18. Different Fortran standards

PropertiesFortran 66Fortran 77Fortran 90Fortran 95
Fixed formFixed formFixedFree(Fixed)Free
Whole Fortran 66=-2-2-2-5-5
Whole Fortran 77-===-5-5
Whole Fortran 90--==-5-5
Whole Fortran 95---14-14==
Continuation line indicated in column 6
on the next line
Continuation line indicated with &
at the end of the present line
Blank line as comment-+++++
Significant blanks---+-+
Generic functions-+++++
User-defined generic functions--++++
Comment symbolCC *C * !!C * !!
Extension in Unix.f.f.f.f90.f.f90
Extension in DOS.FOR.FOR.FOR.F90.FOR.F90

Above, for example, -2 in the position Whole Fortran 66 / Fortran 90 means that two properties have disappeared at the transition from Fortran 66 to Fortran 90. This applies to both fixed form and free form source code.

In the first four lines an equality sign = indicates that nothing has changed, a minus - that several properties are missing.

In the following seven lines a plus + indicates that the property is present, a minus - that it is absent.

Fixed form of the source code is discouraged in Fortran 95!

REAL*8 is an alternative to DOUBLE PRECISION, introduced by IBM and used also by Digital. Several variants exist.

As comment symbol the exclamation mark ! is recommended, it is valid also in several implementations of Fortran 77.

In UNIX there is no concept called extension, and the extensions are not specified in the Fortran standard, but in informal manufacturer standards.

Last modified: 5 December 1995