Developer Guide and Reference

ID 767251
Date 10/31/2024
Public
Document Table of Contents

PRESENT

Inquiry Intrinsic Function (Generic): Returns whether or not an optional dummy argument is present, that is, whether it has an associated actual argument.

result = PRESENT (a)

a

(Input) Must be an argument of the current procedure and must have the OPTIONAL attribute. An explicit interface for the current procedure must be visible to its caller; for more information, see Procedure Interfaces.

Results

The result is a scalar of type default logical. The result is .TRUE. if a is present; otherwise, the result is .FALSE..

Example

Consider the following:

MODULE MYMOD CONTAINS SUBROUTINE CHECK (X, Y) REAL X, Z REAL, OPTIONAL :: Y ... IF (PRESENT (Y)) THEN Z = Y ELSE Z = X * 2 END IF END SUBROUTINE CHECK END MODULE MYMOD ... USE MYMOD CALL CHECK (15.0, 12.0) ! Causes Z to be set to 12.0 CALL CHECK (15.0) ! Causes Z to be set to 30.0

The following shows another example:

CALL who( 1, 2 ) ! prints "A present" "B present" CALL who( 1 ) ! prints "A present" CALL who( b = 2 ) ! prints "B present" CALL who( ) ! prints nothing CONTAINS SUBROUTINE who( a, b ) INTEGER(4), OPTIONAL :: a, b IF (PRESENT(a)) PRINT *,'A present' IF (PRESENT(b)) PRINT *,'B present' END SUBROUTINE who END