(The following information augments or overrides the information in Section 1.5 of ANSI X3.9-1978 FORTRAN 77 in specifying the GNU Fortran language. Chapter 1 of that document otherwise serves as the basis for the relevant aspects of GNU Fortran.)
In this chapter, “must” denotes a requirement, “may” denotes permission, and “must not” and “may not” denote prohibition. Terms such as “might”, “should”, and “can” generally add little or nothing in the way of weight to the GNU Fortran language itself, but are used to explain or illustrate the language.
FROBNITZstatement must precede all executable statements in a program unit, and may not specify any dummy arguments. It may specify local or common variables and arrays. Its use should be limited to portions of the program designed to be non-portable and system-specific, because it might cause the containing program unit to behave quite differently on different systems.”
Insofar as the GNU Fortran language is specified,
the requirements and permissions denoted by the above sample statement
are limited to the placement of the statement and the kinds of
things it may specify.
The rest of the statement—the content regarding non-portable portions
of the program and the differing behavior of program units containing
FROBNITZ statement—does not pertain the GNU Fortran
That content offers advice and warnings about the
Remember: The GNU Fortran language definition specifies both what constitutes a valid GNU Fortran program and how, given such a program, a valid GNU Fortran implementation is to interpret that program.
It is not incumbent upon a valid GNU Fortran implementation to behave in any particular way, any consistent way, or any predictable way when it is asked to interpret input that is not a valid GNU Fortran program.
Such input is said to have undefined behavior when interpreted by a valid GNU Fortran implementation, though an implementation may choose to specify behaviors for some cases of inputs that are not valid GNU Fortran programs.
Other notation used herein is that of the GNU texinfo format, which is used to generate printed hardcopy, on-line hypertext (Info), and on-line HTML versions, all from a single source document. This notation is used as follows:
Note that, in practice, many Fortran programs are written in lowercase—uppercase is used in this manual as a means to readily distinguish keywords and sample Fortran-related text from the prose in this document.
Generally, uppercase is used for all Fortran-specific and Fortran-related text, though this does not always include literal text within Fortran code.
For example: PRINT *, 'My name is Bob'.
INTEGER ivar statement specifies that
ivar is a variable or array of type
In the above example, any valid text may be substituted for the metasyntactic variable ivar to make the statement apply to a specific instance, as long as the same text is substituted for both occurrences of ivar.
See Kind Notation, for information on the relationship
between Fortran 90 nomenclature (such as
and the more traditional, less portably concise nomenclature