MPE/iX Intrinsics Reference Manual (32650-90875)

20 Chapter2

Intrinsic Use

Parameters

Intrinsic parameters can be input, output, or input/output (I/O) parameters:

• Input parameters pass values into the intrinsic routine.

• Output parameters return values from the intrinsic routine to the calling routine.

• I/O parameters pass values into and return values from the intrinsic routine.

Parameter Declarations

Parameters are passed to an intrinsic either by value or by reference, depending on how

the parameter is declared. When a parameter is passed by reference, its address in the

caller's data area is made available to the called procedure. When a parameter is passed by

value, the called procedure receives a private copy of the actual data value. If the called

procedure changes the private copy, the corresponding value in the calling routine remains

unchanged.

Parameters can be either a literal value or a variable; however, only variables can be

passed to reference parameters.

A process must call intrinsic parameters in the exact calling sequence (order) speciﬁed in

the syntax statement and must separate them by commas. For example, write a call to the

CLOSELOG intrinsic as follows:

CLOSELOG(ACCESS,0,0);

You must represent optional intrinsic parameters if they are missing. To indicatea missing

parameter within the parameter list, omit the parameter, but retain the preceding

commas. For example, write a call to the FOPEN intrinsic and omit the second (optional)

parameter as follows:

FILENUM:=FOPEN(MYFILE,,3);

If you omit the ﬁrst parameter from a list, indicate this by following the left parenthesis

with a comma ((,). If you omit one or more parameters from the end of a list, indicate this

by following the last parameter with the right parenthesis; no commas are required.

NOTE

When a process calls an intrinsic with no parameters from C/XL, follow the

intrinsic name with an empty pair of parentheses (()).

Parameter Alignment

For programs running under MPE V and in compatability mode (CM), parameters are

passed by word address, which automatically enforces parameter alignment.

For programs running in native mode (NM), byte addressing is used for all parameters. As

a result, it is possible to pass a 16-bit or 32-bit parameter that is not 16-bit or 32-bit

aligned. Unless explicitly stated in the parameter description, native mode programs do

not impose alignment requirements.