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Thanks for the reply. However, I don't really understand how it works... Can you help? How should this function look like? Can I still create the type the same way I did for now and add something like this: Datum mpoint_in(PG_FUNCTION_ARGS) { char *str = PG_GETARG_CSTRING(0); mPoint *result; mPoint *finalResult; result = (mPoint *) create_mPoint(str); if (result == NULL) { Log ("mpoint_in: reporting error for invalid input syntax for mPoint"); ereport(ERROR, (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION), errmsg("invalid input syntax for mPoint: \"%s\"", str))); } finalResult = (mPoint *)palloc(VARSIZE(result)); memset (finalResult, 0, VARSIZE(result)); SET_VARSIZE(finalResult, VARSIZE(result)); memcpy((void *) VARDATA(finalResult), (void *) VARDATA(result), VARSIZE(result) - VARHDRSZ); PG_RETURN_POINTER(finalResult); } I should still return Datum, right? At least version 1 calling convetion says that. And should I change something on the SQL side? I would appreciate any help. Thanks. Ivan > Date: Thu, 13 May 2010 12:42:09 +0200 > From: kleptog@xxxxxxxxx > To: i.bre@xxxxxxxx > CC: dalroi@xxxxxxxxxxxxxxxxxxxxxxxxxxxx; pgsql-general@xxxxxxxxxxxxxx > Subject: Re: [GENERAL] Persistence problem > > On Thu, May 13, 2010 at 12:04:56PM +0200, I. B. wrote: > > > > > > I'll try to explain with as less code as possible. > > One of the types I wanted to create is called mpoint. This is a part of code: > > <snip> > > > typedef struct { > > int4 length; > > int noOfUnits; > > void *units; // this is later casted to uPoint * > > } mapping_t; > > > > This is not the correct way to handle varlena types. You can create the > datum that way, but if PostgreSQL decides to compress it (as it may > when writing to disk) you won't be able to read it back. Notably, the > "length" part of a varlena type is not always 4 bytes. > > Make sure you have fully understood this page: > http://www.postgresql.org/docs/8.4/static/xfunc-c.html > it has a number of examples dealing with variable length types. You > MUST use the VARDATA/VARATT/etc macros to construct and read your data. > > Hope this helps, > -- > Martijn van Oosterhout <kleptog@xxxxxxxxx> http://svana.org/kleptog/ > > Patriotism is when love of your own people comes first; nationalism, > > when hate for people other than your own comes first. > > - Charles de Gaulle Hotmail: Free, trusted and rich email service. Get it now. |
