RE: [cx-oracle-users] Re: Choosing client libraries

[Amaury F. <Ama...@gl...>]

Anthony wrote:
> To understand what I mean, try loading a cx_Oracle module compiled=20
> against Oracle 9i with an Oracle 8i client. You will get a=20
> messagebox indicating that the symbol OCISessionGet could=20
> not be located in oci.dll. If you have a suggestion about how=20
> to get around that problem __without__ involving a huge=20
> rewrite of cx_Oracle to call everything dynamically I'm all ears.

This is what I did some years ago with the old OCI7 function.
At the time, it was the only way to have a program run with=20
both Oracle7 and Oracle 8i, even if you use only functions=20
that belong to both libraries.

My solution is:
- cx_Oracle does not link with any Oracle library.
- instead, we provide an implementation for each OCI* function,
which simply loads dynamically the Oracle client, bind the
function, and call it.
(I just counted 54 different OCI functions in cx_Oracle!)

Below is a sample, for the old 'olog' function.

This change would not touch any existing cx_Oracle file,
Only one more file is compiled and linked with cx_Oracle.

I think the same trick would also work on some other platforms.
At the end, we could have a "dynamic" version of cx_Oracle!

-----------------------------

typedef sword (*OCIPROC)();
HINSTANCE hOCI =3D NULL;

// Find the OCI library
HINSTANCE check_dll()
{
  // This could be enhanced to choose the desired library
  if (!hOCI) hOCI =3D LoadLibrary("oci.dll");
  return hOCI;
}

// Load the OCI library and find the function
OCIPROC check_function(char *name, OCIPROC *fn)
{
  if( *fn ) return *fn;
  if( !check_dll() ) return NULL;
  *fn =3D (OCIPROC)GetProcAddress( hOCI, name );
  return *fn;
}

// All OCI functions must be written like this
sword olog(LDA *lda, ub1 *hda, text *uid, sword uidl,
text *pswd, sword pswdl, text *conn, sword connl, ub4 mode)
{
  static OCIPROC p_olog=3DNULL;
  if( check_function("olog", &p_olog))
    return p_olog(lda,hda,uid,uidl,pswd,pswdl,conn,connl,mode);
  else
    return 1; // error
}

--=20
Amaury Forgeot d'Arc
Ubix Development
www.ubitrade.com