Thanks for the tips! They will be very usefull!

Regards,

Fabiano

On Tue, Nov 18, 2008 at 9:23 PM, woodsmailbox
<cosmin.apreutesei@...>wrote:

> > Is there some tutorial or guide do develop a multiplataform UDF
> using
> > pascal?
> >
>
> here's my mostly empirical findings and assumptions. btw please
> correct what's wrong (again, only tested with fpc on linux).
>
> #
> #
> # General tips:
> # - by default, all input and output parameters are pointers, so `by
> reference' is the implicit calling method.
> # - if you never return null, use the `by value' calling method to
> avoid having to malloc the result.
> # - when returning `by reference', malloc() the result yourself, and
> declare the udf with the `free_it' directive. for this to work
> # you have to use either clib's malloc() (on linux), msvcrt's malloc()
> (on windows) or ib_util's ib_util_malloc() (cross-platform -- just a
> wrapper o'doze).
> # - in case your udf takes cstring(N) as the <n>'th parameter and
> returns cstring(at most N) of the same charset as that parameter,
> # use `returns parameter <n>' instead, and just write on it's buffer
> instead of malloc'ing another block.
> # Null handling:
> # - firebird 2.0+ will pass nulls as null pointers but only for
> parameters declared as `by reference null'.
> # otherwise you'll get a 0 (zero) for an integer or double parameter,
> and an empty string for a string parameter.
> # - null parameters can also be detected with the `by descriptor'
> calling method.
> # - returning a nil pointer is interpreted as null (note that you
> can't say `returning ... by reference null'; tested in 2.1.1).
> # Type mapping (firebird-freepascal):
> # INTEGER BY REFERENCE - var Longint or PLongint if you want to
> catch/return nulls
> # INTEGER BY VALUE - Longint
> # DOUBLE PRECISION BY REFERENCE - var Double or PDouble if you
> want to catch/return nulls
> # DOUBLE PRECISION BY VALUE - Double
> # CSTRING(N) BY REFERENCE - PChar
> # CSTRING(N) BY VALUE - doesn't make sense
> # <anything> BY DESCRIPTOR - PParamDsc
> # Charsets:
> # - firebird gives/expects text parameters in the charsets the udf was
> declared with.
> # - gotcha: you won't be able to catch/return strings containing
> ascii_char(0) characters except with the `by descriptor'
> # with `varchar by reference' (instead of cstring), you get the length
> at PLongint(param)^ and the contents at @param[2].
> # Using descriptors:
> # - declaring parameters as `<datatype> by descriptor' won't guarantee
> you that the engine will give you the values in that datatype!
> # instead you gotta check dsc_dtype yourself and interpret the value
> accordingly. the advantage is you can write polymorphic functions.
> #
>
>
>
>
>
> ------------------------------------
>
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>
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> on the main (top) menu. Try Knowledgebase and FAQ links !
>
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>
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>

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