| Re: Zeiger in IDL -> call by reference in I [message #4240] |
Thu, 11 May 1995 00:00 |
lmudge
Messages: 9
Registered: October 1994
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Junior Member |
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In article 2tq@hpl.hp.com, peter@hpl.hp.com (Peter Webb) writes:
> Karl Krieger (kak@ipp-garching.mpg.de) wrote:
> : css@ipp-garching.mpg.de writes:
>
> : >Weiss jemand, ob in IDL eine Pointeruebergabe moeglich ist,
> : >(aehnlich wie in C) ? Ansonsten sind ja staendig riesige
> : >Commonbloecke vonnoeten.
>
> : After reading this guys question (if it was possible to pass variables
> : by reference in IDL) I read the fine manual on that subject which leads
> : me to another question:
> : They state that if you pass a variable to a procedure, it is saved in a
> : temporary location. When returning from the procedure, the new parameter
> : values are copied back into the corresponding variables.
> : Does this really mean that IDL allocates new memory for each parameter
> : variable even when calling by refernce i.e. passing a pointer?
>
> It says that in the manual, but it isn't true. If you allocate big
> arrays till you run out of memory, then try passing that big array to a
> subroutine which, say, prints a single element, the call will succeed,
> indicating that the array was not copied.
>
> I guess the manual is a convoluted attempt to explain `pass by
> reference' to newbies.
>
> Peter
>
> --------------------------------
> Peter Webb, HP Labs Medical Dept
> E-Mail: peter_webb@hpl.hp.com
> Phone: (415) 813-3756
Using handles in IDL (new to version 3.6.1a) seems to be a way of passing
large arrays to subroutines by reference. Each handle has a handle id which
is a unique 32 bit longword integer allocated by IDL. My guess is that this
value is a pointer to a memory location that contains details of the variable
contained in the handle and a pointer to the memory location where the data
is stored.
Leith Mudge
------------------------------------------------------------ --------------------
lmudge@awadi.com.au
AWA Defence Industries
PO Box 161
Elizabeth SA 5112
+61 8 256 0952
Microsoft Network is prohibited from redistributing this work in any form,
in whole or in part. Copyright, Leith Mudge, 1995
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