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Thanks for the reply. Why is that somewhere else in the memory if I reserve enough memory with palloc and copy the complete memory from the previously created type into that new object? realResult = (mPoint *)palloc(result->length); memcpy(realResult, result, result->length); OK, I suppose I should use the VARDATA and VARSIZE. But I really can't make it to work. I don't think I understood well enough how it works. This is what I'd like to do. I would like to create the type as I already did, and when it's created I would like to copy its memory into a new object. So, if I have: Datum mpoint_in(PG_FUNCTION_ARGS) { char *str = PG_GETARG_CSTRING(0); mPoint *result = (mPoint *) create_mPoint(str); mPoint *final result = ... //copy the memory from result PG_RETURN_POINTER(result); } Datum mpoint_out(PG_FUNCTION_ARGS) { mPoint * input = (mPoint *) PG_GETARG_POINTER(0); char * result = ToString (input, MPOINT); PG_RETURN_CSTRING(result); } Can you please help me to make this? How to copy the memory in a good way? Should I somehow change the type mPoint? Should I also change the SQL side? CREATE TYPE mpoint ( internallength = VARIABLE, input = mpoint_in, output = mpoint_out ); Please help, it would mean a lot. Thanks, Ivan > To: i.bre@xxxxxxxx > CC: kleptog@xxxxxxxxx; dalroi@xxxxxxxxxxxxxxxxxxxxxxxxxxxx; pgsql-general@xxxxxxxxxxxxxx > Subject: Re: Persistence problem > Date: Thu, 13 May 2010 15:08:58 -0400 > From: tgl@xxxxxxxxxxxxx > > "I. B." <i.bre@xxxxxxxx> writes: > > When I do this: > > realResult = (mPoint *)palloc(result->length); > > memcpy(realResult, result, result->length); > > I get a right result in the same session, but corrupted in the next > > one. > > I'm guessing a bit here, but I think what is happening is this: > > > typedef struct { > > int4 length; > > int noOfUnits; > > void *units; // this is later casted to uPoint * > > } mapping_t; > > You're storing the above-named struct on disk, right? And the "units" > pointer is pointing to an array that's somewhere else in memory? As > long as the somewhere-else array survives, it will seem like everything > is okay. But in a new session, that data in memory will certainly not > be there anymore. > > You can't use pointers in data structures that are to be stored on disk. > The array data needs to be "in line" in the data structure, and > accounted for in the length word. > > Martin's advice about using VARSIZE/VARDATA is good too. Depending on > which PG version you're using, you might be able to get along without > that so long as you haven't marked the data type toastable (by using > a non-PLAIN storage option in CREATE TYPE). But unless that array is > always pretty darn small, you're going to want to allow this type to > be toasted. > > regards, tom lane Hotmail: Trusted email with Microsoft’s powerful SPAM protection. Sign up now. |
