Parameters
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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 DeclarationsParameters 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 indicate a 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.
Parameter AlignmentFor 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. Parameter Bit SettingsIn some intrinsic calls, a process passes input parameters to the intrinsic as words whose individual bits or fields of bits signify functions or options. In cases where bits within a word are described as reserved for the operating system, set those bits to zero. This ensures the compatibility of your current program with future releases of the operating system. In some intrinsic calls, an intrinsic passes output parameters to words referenced by a calling program. In cases where bits within a word are described as reserved for the operating system, the system sets them to zero unless otherwise noted. Syntax Statement MnemonicsAn intrinsic's syntax statement contains the calling sequence, or order, of the parameters, indicates whether a parameter is required or optional, and specifies the parameter type. Syntax statements have the following format:
I16V U16V
ACTIVATE (pin, allow);
Required parameters, such as pin in the example above, appear
in boldface italics. Optional parameters, such as
allow, are shown in italics. The mnemonics that
appear over the parameters indicate their type and whether they are passed by
reference, which is the default, and is not marked, or by value. (In the
example, the mnemonics for both parameters have a V, which indicates
that they are passed by value.)
The next table lists the mnemonics used in intrinsic syntax statements and
their meanings.
Table 2-1 Mnemonic Descriptions
Itemnum and Item Pair OptionsSome intrinsics allow multiple itemnum,item pairs to be passed to define one or more options. The itemnum parameter is usually an integer value that the intrinsic uses to define the meaning and the expected data type of the value passed or returned in the corresponding item parameter. An itemnum cannot be passed without its corresponding item value. The only exception is when a special value is passed in the last itemnum to indicate the end of the itemnum,item list; in this case, an accompanying item is not required. Data Type MappingsTable 2-2 "Data Type Mappings" maps generic data types to possible implementations in programming languages supported by the operating system. The mnemonics associated with the generic types appear in parentheses. For more information on calling intrinsics from these languages, refer to the appropriate language reference manual.
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