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From: jason@ux1.cso.uiuc.edu (Jason)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Two (2) weenie C questions...
Message-ID: <1990Sep6.164746.7215@ux1.cso.uiuc.edu>
Date: 6 Sep 90 16:47:46 GMT
References: <202759@<1990Aug29> <53100021@uxh.cso.uiuc.edu>
Organization: University of Illinois at Urbana
Lines: 46

johnsone@uxh.cso.uiuc.edu writes:


>/* Written  2:21 pm  Aug 29, 1990 by gft_robert@gsbacd.uchicago.edu  */
>>2) How does one return a Str255 from a function?  THINK complains "can't return
>>array from function"?  But aren't I returning a pointer to the first (Oth) char
>>of the Str255 if I "return myString"?  Do I need Str255 *MyProc() if I want to
>>pass back any reference to a Str255 at all?

>I was going to suggest declaring the function:

>       char *MyProc()

>but I just tried it and it doesn't work.  Using this will work:

>       MyProc( Str255 myString )

>called with:

>       Str255 aString;

>This doesn't give you a function, but it may serve your purpose.


	In a Think C function, if you make a declaration of the form:

        	type	anArray[ A_SIZE ];

the compiler will not allow such an array to be returned to the calling
function because the return value would point to the first character of
the array--an array whose memory space was allocated on the stack
_temporarily_ and which is released when the function returns.  Therefore,
a pointer returned in this way actually points to an undefined object and
is not usable.  The above method ( MyProc( Str255 myString ) ) works because
the object being passed to MyProc() is declared in the calling function
(or in that function's calling function, etc., or globally) giving it a
broader "scope" than this occurrance of the function MyProc().  In other words,
myString is good for more than just the duration of MyProc().  If you *really*
want a function to return an array, its storage can be allocated on the heap
using NewPtr() or NewHandle().  This method is unwise, so I won't go into the
complications it presents.
-- 

                       |  |    |====================|
                       |  |    | Jason Watts        |
                     \ |\ |\ \ | (jazzin@uiuc.edu)  |