Intel fortran-80 manual Common Blocks, Dummy And Actual Arguments, Association Of Arguments

FORTRAN-80 Functions And Subroutines

5.3.1 Common Blocks

Common blocks reduce storage requirements by allowing two or more subprograms to share the same memory. This sharing may be limited by the rules for defining and referencing data.

The variables and arrays in a common block can be defined and referenced in all subprograms that contain a declaration of that common block. 'Association is by memory location rather than by name, so the names of variables and arrays of a given common block may be different in the different subprograms. However, the data referenced and the common block name used to reference the data must be of the same type.

An integer variable ASSIGNed a statement label can only be referenced in the pro- gram unit containing its ASSIGN statement.

5.3.2 Dummy And Actual Arguments

A dummy argument is used in the argument list when defining a procedure. An ac- tual argument is used in the corresponding argument list when the procedure is referenced.

Dummy arguments are used by statement functions, FUNCTION subprograms, and SUBROUTINE subprograms to specify the types of actual arguments and whether the argument is a single value, array, or procedure. In the case of a statement func- tion, the dummy argument must be a variable.

Dummy argument names can be used anywhere an actual name of the same 'class' (that is, variable, array, or dummy procedure) and type can be used, unless explicitly prohibited. Dummy argument names cannot appear in EQUIVALENCE, DATA, SA VE, INTRINSIC, or COMMON statements (except as common block names). A dummy name also cannot be the same as a FUNCTION, SUBROUTINE, or state- ment function name declared in the same program unit.

Actual arguments list the entities to be associated with corresponding dummy arguments for a particular procedure reference. Actual arguments may be constants, function or subroutine references, or expressions, including parenthesized expres- sions (if the associated dummy argument is not defined during execution of the ex- ternal procedure). An actual argument cannot be the name of a statement function defined later in the program unit containing the reference.

5.3.3 Association Of Arguments

When a procedure reference is executed, the actual and dummy arguments are associated; the first actual argument replaces all occurrences of the first dummy argument, etc. Therefore, the arguments must agree in order, number, type (except when the actual argument is a subroutine name), and length (where applicable).

If an actual argument is associated with a dummy appearing in an adjustable dimen- sion, the actual argument must be defined with an integer value when the procedure is referenced.

If an actual argument is an expression, the expression is evaluated before associa- tion. If the actual is an array element name, its subscript is evaluated before associa- tion.

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