Date:	Mon, 13 Jan 1997 16:04:25 -0200
Message-Id:	<1.5.4.16.19970113132927.28df398e@dmeasc.rc.ipt.br>
Mime-Version:	1.0
To:	combee AT cambridge DOT scr DOT slb DOT com (Leendert Combee),
	glynnec AT ix DOT netcom DOT com (Glynne Casteel)
From:	Cesar Scarpini Rabak <csrabak AT dce03 DOT ipt DOT br>
Subject:	Re: f2c+djgpp
Cc:	djgpp AT delorie DOT com

At 10:43 13/01/97 +0000, Leendert Combee wrote:
>> This is no cause for concern; a does not need to be reset!  The reason
>> is that it is passed in as a pointer to the function.  Something like
>> [I assume]: 
>> 
>>    void test( double *a, int n )
>>    {
>>     /* decrementing a here has no effect on its value 
>>      * in the calling program!!
>>      */
>>     a--;  /* calling program cannot see this */
>> 
>>     /* HOWEVER changing the values that it points to 
>>      * will be reflected in the calling program
>>      */
>>     a[1] = 16.0;   /* calling program CAN see this change */
>> 
>>    }
>> 
>
>  No!, on return a[i] correspond now to a[i+1] before the function was called
>  (+whatever happened in the function). Because a (not *a) is a pointer, 
>  --a changes that value!  The code generated by f2c shoudl really use
>  a_new-- = a ; and then work with a_new rather than a. This causes that
>  a[i] still points to same element of a before _and_after the function
>  call !!
>
>  Leendert
>
Do you have test cases to support evidence on this? The pointer passed as
parameter in the function is _a copy_ of the pointer sent as argument, so
Casteel's comments seem correct, except if the C compiler you use afterwards
in the generated code decides to "optimize" so much to use the same memory
position!
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Cesar Scarpini Rabak                      E-mail: csrabak AT ipt DOT br
DME/ASC                                   Phone: 55-11-268-3522 Ext.350
IPT - Instituto de Pesquisas Tecnologicas Fax:   55-11-268-5996
Av. Prof. Almeida Prado, 532.  Sao Paulo - SP 05508-901 BRAZIL
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- Raw text -