RE: Constants (was: *varsize array as procedure parameter)

Bob, 
 
So if I understand right, when I declare a procedure:

     p Search          B 
     d Search          PI             5U 0 
     d  peArray                            likeds(bigDS)
     d                                     dim(32767) 
     d                                     const
     d                                     options(*varsize) 

And I have in the calling program a global array declared :

     d bigDS           DS
     d   field1                   32767A
     d   field2                   32767A     
     d ArrayToPass     S                   likeds(bigDS)
     d                                     dim(3000)

That would cause the compiler to create a temporary array because
ArrayToPass is a fixed length field ?

TIA, Arco Simonse


> -----Oorspronkelijk bericht-----
> Van: rpg400-l-bounces@xxxxxxxxxxxx 
> [mailto:rpg400-l-bounces@xxxxxxxxxxxx] Namens Bob Cozzi
> Verzonden: zaterdag 3 september 2005 17:22
> Aan: 'RPG programming on the AS400 / iSeries'
> Onderwerp: RE: Constants (was: *varsize array as procedure parameter)
> 
> Birgitta,
> 
> When CONST is specified for a parameter and VARYING is also 
> specified, a copy of the input parameter's value is made if:
> A) The input value is in a fixed-length field.
> B) The input value is in a VARYING field and it is shorter 
> than the declared parameter length.
> C) A literal or character-string expression is passed.
> 
> And probably one or two other situations that I can't think of.
> 
> My rule-of-thumb is to always use CONST for numeric 
> parameters and date parameters (obviously if I don't need to 
> modify them). And for character parameters, justify why I 
> don't need it, otherwise use CONST there too.
> Again, the only caveat to this is when VARYING is used.
> 
> Also, you don't want to use long return values from 
> procedures--this kills performance. An integer or very short 
> character value is fine, but returning something like a data 
> structure or worse data structure array or just an array is a 
> performance killer... Instead, pass a parameter, update it, 
> and return perhaps the number of value populated in the array 
> as an integer.
> 
> -Bob Cozzi
> www.RPGxTools.com
> RPG xTools - Enjoy programming again.
> 
> 
> -----Original Message-----
> From: rpg400-l-bounces@xxxxxxxxxxxx 
> [mailto:rpg400-l-bounces@xxxxxxxxxxxx]
> On Behalf Of HauserSSS
> Sent: Saturday, September 03, 2005 3:54 AM
> To: RPG programming on the AS400 / iSeries
> Subject: AW: Constants (was: *varsize array as procedure parameter)
> 
> Hi David,
> 
> >>If a const is just a pointer to a variable that isn't allowed to be 
> >>changed ... is there any reason I couldn't take the address of that 
> >>pointer, assign it to another (non-const) variable, and change the 
> >>const's value that way?
> 
> May be we should explain what happens if a parameter is 
> passed by constant
> reference:
> If the passed parameter has the same data type and length as 
> required in the prototype, the address of this parameter 
> field is passed to the called procedure.
> If the passed parameter has a compatible data type or 
> different length, a temporary field with the required 
> definition is created and initialized with the parameter 
> value. After the address of this temporary field is passed to 
> the called procedure.
> Because it cannot be determined whether the received address 
> is from the original field or a temporary field, and to avoid 
> to change some values by mistake, it's forbidden to change a 
> parameter field that is passed by constant reference.
> The compilers already check it.
> 
> Birgitta
> 
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