Attempts at creating an embedded mySQL DLL for VB:
I can successfully use the mysql_init() function from libmysql.lib to create
a DLL for VB. However, when I use this function (in a DLL or lib)linked
against the libmysqld.lib or mysqlserver.lib it crashes the VB application
but not the C application.
I tried hard coding the arguments and servergroups for mysql_server_init (I
also used memset to initialize the strings to 0), I get the same result.
The lib I create will always work with a C program, but the DLL will not
work with VB.
Does anyone have any more suggestions on how to use the embedded library in
a Visual C DLL to link with VB?
Thanks
Eric
p.s: Email received from another individual (Thanks!!):
Put the libMySql.dll in the wint\system32 directory (or in the directory
where
your executable is!)
In vb, I use this one
the declares:
Public Declare Function mysql_init Lib "libmySQL" (ByVal lMYSQL As Long)
As
Long
Public Declare Function mysql_real_connect Lib "libmySQL" _
(ByVal lMYSQL As Long, _
ByVal sHostName As String, _
ByVal sUserName As String, _
ByVal sPassword As String, _
ByVal sDbName As String, _
ByVal lPortNum As Long, _
ByVal sSocketName As String, _
ByVal lFlags As Long) As Long
Public Function OpenConnection(ByVal sHostName As String, _
ByVal sUserName As String, _
ByVal sPassword As String, _
ByVal sDbName As String, _
Optional ByVal lPortNum As Long = 3306, _
Optional ByVal lFlags As MYSQL_FLAG) As
MYSQL_CONNECTION_STATE
........
mlMYSQL = mysql_init(mlMYSQL)
If mlMYSQL = 0 Then
no connection handler
Else
'connect to server
If mysql_real_connect(mlMYSQL, msHostname, msUsername, msPassword,
msDbName, mlPortNum, "", mlFlags) = 0 Then
' oops
Else
'connection established ... state is now open
End If
End If
'setup the return value
End Function
I myselve created an dll (in vb) which encapsulates all the stuff to connect
to
the database, use recordsets, .... (as close as possible to the ADO object
model: so with connection, recordset - objects,
bookmarks, fields, ...)
Hope this helps.
From: "Gelu Gogancea" <ggelu@xxxxxxxxx>
To: "Derick Smith"
<niagara_man@xxxxxxxxxxx>,<mysql@xxxxxxxxxxxxxxx>,<win32@xxxxxxxxxxxxxxx>
Subject: Re: HELP mysql_server_init embedded in a DLL?
Date: Fri, 28 Feb 2003 14:40:31 +0200
Hi,
----- Original Message -----
From: "Derick Smith" <niagara_man@xxxxxxxxxxx>
To: <mysql@xxxxxxxxxxxxxxx>; <win32@xxxxxxxxxxxxxxx>
Sent: Thursday, February 27, 2003 10:33 PM
Subject: Re: HELP mysql_server_init embedded in a DLL?
> I am posting this again, in hope that I will get a response.
>
> I tried doing the following (see VB code below. I got this code from
another
> site):
>
> I get the same error message as if I was calling the DLL I created in C
> which calls mysql_server_init.
>
> Is it impossible to call this function from VB or embedded in another
DLL
> from VB?
> Can I only use the embedded mysql library in C or C++?
>
> Thanks
> Eric
>
> Public Declare Function mysql_server_init Lib
> "C:\mysql40\source\lib_release\libmysqld.dll" _
> (ByVal argc As Long, _
> ByVal argv As Byte, _
> ByVal groups As Byte) As Long
>
> Private Sub cmdmysq_server_init_Click()
> Dim argv(0) As Byte, groups(0) As Byte
> Dim i As Long
> argv(0) = Asc("0")
> groups(0) = Asc("0")
> i = mysql_server_init(0, argv, groups)
> End Sub
In my opinion,this will never work because argv and groups are pointed to
array which have a pointer ....char*(*);
But anyhow...if you wish to try again this formula, must declare argv and
groups ByRef because VB is responsable for the stack and the variable must
be initialized before using like argument in function.Since argv and
groups
are byte is a non-sense to use ASC().
I'm very pessimistic that will be work.
>
>
>
>
> >From: "Derick Smith" <niagara_man@xxxxxxxxxxx>
> >To: mysql@xxxxxxxxxxxxxxx, win32@xxxxxxxxxxxxxxx
> >Subject: mysql_server_init embedded in a DLL?
> >Date: Wed, 26 Feb 2003 14:34:28 +0000
> >
> >Hi!
> >
> >I am trying to create a DLL that will hide embedded mySQL functions for
use
> >with VB. I am using mysqlserver.lib. I am able to compile and execute
the
> >following code. This has to be done in C because VB is too slow :-(
> >
> >If mysql_server_init function is run in the DLL from Visual Basic. I
get
> >the following error message: "..referenced memory at "0x000000". The
> >memory could not be read".
> >
> >Without the mysql_server_init function it will run correctly. It will
also
> >run correctly when this is compiled as a .lib file linked to a C
program.
> >
> >Is it possible to embed mysql_server_init in a DLL? (So the DLL can be
used
> >in VB)
> >
> >Thanks in advance for any responses.
> >
> >Thanks
> >Eric
> >
> >
> >header1.h
> >
> >#define GPAPI __stdcall
> >
> >header2.h
> >
> >typedef unsigned long DBS;
> >#define NULLDBS (DBS)0
> >
> >api.c
> >
> >GPAPI DBS dbNewSet (char * basedir, char * datadir, char * dbname)
> >{
> > return NewSet(basedir,datadir,dbname);
> >}
> >
> >
> >newset.c
> >
> >extern DBS NewSet(char * basedir, char * datadir, char * dbname)
> >{
> > DBSET* pSet = CreateSet();
> > char *args[3];
> > char strArgs[3][1024];
I guess some problems can be elimanted if you initialize the variables
which
are declared or if you allocate some memory.
Anyhow you can use '\0' - termination string to be sure that you don't have
*other garbage* after your string.This *garbage* can influence the lenght
of the string.Bad thing.
> > int iRtn;
> > int argc = 3;
> >
> > strcpy(strArgs[0],"this_program");
> > sprintf(strArgs[1],"--basedir=%s",basedir);
> > sprintf(strArgs[2],"--datadir=%s",datadir);
> > args[0]= strArgs[0];
> > args[1]= strArgs[1];
> > args[2]= strArgs[2];
> >
> >/* If I comment out this line of code,
> >the DLL will run correctly.
> >If mysql_server_init function is run in the DLL. I get the following
> >error message: "..referenced memory at "0x000000". The
...this means that one of your variables is NULL.This error occur because
you don't *catch* the right pointer.By using equal sign you pass the
pointer
to lvalue and not the value.At the address of pointer you can find the
value.
> >memory could not be read" */
> > iRtn = mysql_server_init(3, args, server_groups);
> >
> > if (pSet ==0 ) return NULLDBS;
> > memset(pSet, 0, sizeof(DBSET)); /* Zero the structure. */
> > pSet->size = sizeof(DBSET);/* Assign structure size. */
> > pSet->magic = DBS_MAGIC; /* Assign magic number. */
> >
> > return (DBS)(void*)pSet;
> >}
If you have a little patience (maybe a week or two...i try to find some
available time for this) a new version of GMySQL(An interface between MYSQL
C API function and VB or other development platform for Windows) will be
released.This new version, will contain the implementation of the new
replication functions and also will be able to work with libmysqld.
Regards,
Gelu
_____________________________________________________
G.NET SOFTWARE COMPANY
Permanent e-mail address : gg@xxxxxxxxxxxxxxxxx
gelugogancea@xxxxxxxxx
>
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