SUBROUTINE statement

Standard: (F77) F90 F95 F2003 F2008 F2018 Example program

＜Syntax＞

[ prefix ] SUBROUTINE name [ ( args ) [ bind-attr ] ]

args ::= [ arg [ , arg ]... ]
arg ::= name | *}

bind-attr ::= BIND ( C [ , NAME=expression ] )

prefix	::=	ELEMENTAL
	\|	IMPURE
	\|	MODULE
	\|	NON_RECURSIVE
	\|	PURE
	\|	RECURSIVE

No more than one of each kind of prefix is allowed in a single SUBROUTINE statement. If IMPURE appears, PURE must not appear. If MODULE appears, the interface or definition must be for a separate module procedure. If NON_RECURSIVE appears, RECURSIVE must not appear.

The SUBROUTINE statement can only occur as the first statement of a subroutine subprogram or interface body. The syntax of a subroutine subprogram is as follows.
subroutine-stmt
specification-part
executable-part
[ contains-stmt
[ internal-subprogram ]... ]
end-subroutine-stmt
An internal-subprogram is a function-subprogram or a subroutine-subprogram, and is not allowed to itself have a contains-stmt.

The syntax of a subroutine interface body is simply:

subroutine-stmt
specification-part
end-subroutine-stmt

＜Semantics＞

The SUBROUTINE statement begins a subroutine subprogram.

Each dummy argument that is * is an alternate return; the corresponding actual argument must be a label (prefixed by ‘*’). It is possible to transfer control to one of these labels on return from a subroutine by including an expression on the RETURN statement; if the expression has the value 1 control is transferred to the first label, etc.. If the expression is less than 1 or more than the number of label arguments, execution continues with the statement following the CALL statement. Alternate returns are error-prone and their use is not recommended.