### 8.8.9.1 %DESCR (VMS only), %REF, and %VAL Argument List Functions

When a procedure is called, Fortran (by default) passes the address of the actual argument, and its length if it is of type character. To call non-Fortran procedures, you may need to pass the actual arguments in a form different from that used by Fortran.

The built-in functions %DESCR, %REF, and %VAL let you change the form of an actual argument. You must specify these functions in the actual argument list of a CALL statement or function reference. You cannot use them in any other context.

These functions specify how to pass an actual argument (for example, a) to a non-Fortran procedure, as follows:

Function | Effect
--- | ---
%VAL (a) | Passes argument a as an n-bit 1 immediate value. If a is integer (or logical) and shorter than n bits, it is sign-extended to an n-bit value. For complex data types, %VAL passes two n-bit arguments.
%REF (a) | Passes argument a by reference.
%DESCR(a) | Passes argument a by descriptor. (VMS only)
1 n is 64 on Alpha and ia64 processors; 32 on ia32 processors.

Table 8-1 lists the Compaq Fortran defaults for argument passing, and the allowed uses of %DESCR, %REF, and %VAL.

Table 8-1 Defaults for Argument List Functions

|  | Allowed Functions
--- | --- | ---
Actual Argument Data Type | Default | %VAL | %REF | %DESCR 1
Expressions:
Logical | REF | Yes 2 | Yes | Yes
Integer | REF | Yes 2 | Yes | Yes
REAL(4) | REF | Yes | Yes | Yes
REAL(8) | REF | Yes 3 | Yes | Yes
REAL(16) 4 | REF | No | Yes | Yes
COMPLEX(4) | REF | Yes | Yes | Yes
COMPLEX(8) | REF | Yes | Yes | Yes
COMPLEX(16) 4 | REF | No | Yes | Yes
Character | DESCR 1,5 | No | Yes | Yes
Hollerith | REF | No | No | No
Aggregate 6 | REF | No | Yes | No
Derived | REF | No | Yes | No
Array Name:
Numeric | REF | No | Yes | Yes
Character | DESCR 1,5 | No | Yes | Yes
Aggregate 6 | REF | No | Yes | No
Derived | REF | No | Yes | No
Procedure Name:
Numeric | REF | No | Yes | Yes
Character | DESCR 1,5 | No | Yes | Yes
1 VMS only 2 If a logical or integer value occupies less than 64 (Alpha and ia64) or 32 (ia32) bits of storage, it is converted to the correct size by sign extension. Use the ZEXT function if zero extension is desired. 3 Alpha only 4 VMS, U*X 5 On Tru64 UNIX, Linux, and Windows systems, a character argument is passed by address and hidden length. (For more information, see your user manual or programmer's guide.) 6 In Compaq Fortran record structures

The %VAL, %REF, and %DESCR functions override related cDEC$ ATTRIBUTE settings.

For More Information:

For details on how to use the %VAL, %REF, and %DESCR functions, see your user manual or programmer's guide.

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