On 6/29/2013 8:29 AM, Paul Gilmartin wrote:
On Sat, 29 Jun 2013 15:28:06 +0200, Bernd Oppolzer wrote:
normally pointers to structures are passed between PL/1 and C,
and these structures are defined (language independent) using a
repository, from which both structure definitions for both languages
are generated (and for ASSEMBLER, too, BTW).
One thing I believe I've noticed about IBM's C is that parameters of
most types are passed by reference: the address of the parameter,
not its value, is passed in the argument list. It's left to the subroutine
to make a copy of the value. However, if the parameter is of a pointer
type, its value, not its address is passed in the argument list.
Confusing. And could produce unexpected results if the programmer
resorts to type punning.
Did I observe correctly?
-- gil
Not entirely.
First, though, I'd like to question your assumption that
if the address of a parameter is passed the subroutine
will make a copy of the value. If an address is passed I
would expect the subroutine to tie the address to a
DSECT / based / linkage section (Assembler / PL/I / COBOL)
structure, thus referencing the data without making a copy.
Passing arguments in C:
* Of course, there is interaction based on the prototype
of the function declaration and how an argument is
specified on the function call, but generally ...
* If you pass the name of a structure, the entire
structure is passed in the argument list
* If you pass the name of any item preceded by an apostrophe
the address of the item is passed in the argument list
(This is true for structures and arrays and elementary items)
* If you pass the name of a pointer preceded by an asterisk,
the value pointed at by the pointer is placed into the
argument list
* If you pass a character literal (e.g.: 'C'), the literal
is placed into a full word in the argument list, right
justified, left filled with nulls
* If you pass a numeric literal or numeric expression, the
expression is converted to the format indicated in the
prototype and placed into the argument list
(of course, the literal or expression must be such that
such a conversion is possible; otherwise you get a
compile error)
* A variable number of arguments may be passed using an
ellipsis (...) in the function prototype
* Note that C never turns on the end-of-list bit unless
you include
#pragma linkage(subroutine_name,OS)
"Cross Program Communication in z/OS" - 3 days
http://www.trainersfriend.com/Language_Environment_courses/m520descr.htm
--
Kind regards,
-Steve Comstock
The Trainer's Friend, Inc.
303-355-2752
http://www.trainersfriend.com
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