Re: [sqlite] Error with xBestIndex

[dave]

Yep, same one as me, glad the info helped.  I think I may file a bug on
that.
Delphi, I do remember that, and have had rare occasion to use it, though
I've never linked c obj in (or are you using sqlite as a dll?).
Good luck on the rest of you implementation!
-dave

> -Original Message-
> From: sqlite-users-boun...@sqlite.org 
> [mailto:sqlite-users-boun...@sqlite.org] On Behalf Of vendomele
> Sent: Wednesday, September 10, 2014 10:01 AM
> To: sqlite-users@sqlite.org
> Subject: Re: [sqlite] Error with xBestIndex
> 
> 
> Thanks a lot Dave
> 
> The problem came from SQLite3_vtab's attributte:  zErrMsg.
> 
> It was not initialized to null.
> 
> Now I have more crashes, I can continue the development of 
> the loadable
> extension.
> 
> For your information, I develop in Delphi, it is not too difficult to
> transcribe C in Delphi
> 
> 
> 
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> View this message in context: 
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808p77820.html
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Re: [sqlite] Error with xBestIndex

[vendomele]

Thanks a lot Dave

The problem came from SQLite3_vtab's attributte:  zErrMsg.

It was not initialized to null.

Now I have more crashes, I can continue the development of the loadable
extension.

For your information, I develop in Delphi, it is not too difficult to
transcribe C in Delphi



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Re: [sqlite] Error with xBestIndex

[vendomele]

Hi Dominique,

Yes I started by creating a user defined function, I followed the example of
the "half" function we can find everywhere on the Internet and it works

My loadable extension manages to create a virtual table when I send the
"CREATE VIRTUAL TABLE x USING ..." SQL command, I can see the newly created
table, but the queries "SELECT ..." with or without "WHERE" do not work. 



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Re: [sqlite] Error with xBestIndex

[vendomele]

Hi Dominique,

Yes I started by creating a user defined function, I followed the example of
the "half" function we can find everywhere on the Internet and it works

My loadable extension manages to create a virtual table when I send the
"CREATE VIRTUAL TABLE x USING ..." SQL command, I can see the newly created
table, but the queries "SELECT ..." with or without "WHERE" do not work.



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Re: [sqlite] Error with xBestIndex

[dave]

I can confirm to Vendomele that implementing a xBestIndex with a 'return
SQLITE_OK;' does work -- I did this myself a few weeks ago.

I do second Dominique's advice about checking the use of the various
'SQLITE_EXTENSION_INITx' macros.  There's three of them.  If it's not
already obvious, what it does is forward the calls of the sqlite functions
to the host application; you should /not/ link your extension with sqlite.c
(which I had done for a while until I understood).

In my case, my lib supports both static and dynamic linkage, and a bunch of
implementation files, so I wind up using all three of those macros.  My
'main' module (which has the init function) is more-or-less like the
documentation; my 'implemenation' (where the actual extension functions,
virtual tables, etc) are, all start with this:

#ifndef SQLITE_CORE
#include "..\sqlite3\sqlite3ext.h"
extern "C" {
//declares extern the vtable of all the sqlite3 functions (for loadable
modules only)
SQLITE_EXTENSION_INIT3
}
#else
#include "../sqlite3/sqlite3.h"
#endif

I didn't find any doc on SQLITE_EXTENSION_INIT3, but it's easy to see it
just defines an extern to the c-style v-table declared in your 'main' module
via SQLITE_EXTENSION_INIT1, and initialized in your init function via
SQLITE-EXTENSION_INIT2.

Debugging advice:  build the sqlite shell project in a debug configuration.
Use that as a test harness for your loadable extension, and then you can
step through the sqlite source and get a better handle on what is crashing.
I had to do this many many times.  Also, I don't know what platform you're
developing on, and what tools you are using, but do use the
split-sqlite3c.tcl to split the amalgamation, so your debugger won't wig on
the huge number of source lines.

Barring all that, you might check your surrounding code.  I myself found
some anomalies, such as:
*  in the xCreate function, the doc states that 'The xCreate method need not
initialize the pModule, nRef, and zErrMsg fields...', however I found that
not to be the case.  I set nRef = 0 (which is not used, but I do it anyway),
and critically important, zErrMsg = NULL;.  That is intended to be a string
containing an error message allocated by a sqlite function
sqlite3_mprintf(), and if it is not null (like, if it is not initialized),
sqlite will eventually attempt to free it, and I experienced crashes when I
was initially developing because of that behaviour.

Good luck!

-dave

> -Original Message-
> From: sqlite-users-boun...@sqlite.org 
> [mailto:sqlite-users-boun...@sqlite.org] On Behalf Of 
> Dominique Devienne
> Sent: Wednesday, September 10, 2014 7:14 AM
> To: General Discussion of SQLite Database
> Subject: Re: [sqlite] Error with xBestIndex
> 
> 
> On Wed, Sep 10, 2014 at 11:53 AM, vendomele <fve...@gmail.com> wrote:
> 
> > I developed a loadable extension, but after the execution 
> of the callback
> > "xBestIndex" there is a crash.
> >
> > So I made it simple for this callback by implementing only 
> one line that
> > returns SQLITE_OK.
> >
> > The crash still persists.
> >
> > With a development tool, the crash occurred in an external 
> instruction to
> > my
> > dll:
> > "dword ptr and [ebp- $ 04] $ 00"
> >
> > Anyone have an idea?
> >
> 
> Can you run a simple user-defined-function from that loadable 
> extension?
> That's a simpler use-case than trying to write a vtable impl.
> 
> Did you use the macros mentioned by 
> http://www.sqlite.org/loadext.html ?
> 
> Those macros ensure that the loaded extension uses the same 
> SQLite code
> than the host program (the .exe on Windows), which can have crashing
> consequences if not properly defined.
> 
> Also, you must typically compile your extension with the same 
> SQLite3 used
> to compile the host app. The API is mostly stable, but that's 
> an obvious
> step to double-check in case of crashes like here. --DD
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Re: [sqlite] Error with xBestIndex

[Dominique Devienne]

On Wed, Sep 10, 2014 at 11:53 AM, vendomele  wrote:

> I developed a loadable extension, but after the execution of the callback
> "xBestIndex" there is a crash.
>
> So I made it simple for this callback by implementing only one line that
> returns SQLITE_OK.
>
> The crash still persists.
>
> With a development tool, the crash occurred in an external instruction to
> my
> dll:
> "dword ptr and [ebp- $ 04] $ 00"
>
> Anyone have an idea?
>

Can you run a simple user-defined-function from that loadable extension?
That's a simpler use-case than trying to write a vtable impl.

Did you use the macros mentioned by http://www.sqlite.org/loadext.html ?

Those macros ensure that the loaded extension uses the same SQLite code
than the host program (the .exe on Windows), which can have crashing
consequences if not properly defined.

Also, you must typically compile your extension with the same SQLite3 used
to compile the host app. The API is mostly stable, but that's an obvious
step to double-check in case of crashes like here. --DD
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