Access violation while trying to update clob

[Anonymous]

Hi,

I am currently switching an application from using Pro*c to using OCILIB.
Everything works fine, except updating clobs.

When trying to update a clob, I always get an access violation in
oracommon9.dll trying to read address 0x45.

An example:

... // Initializing connection
OCI_Statement* stmt = OCI_StatementCreate(conn);
OCI_Prepare(stmt, "UPDATE tbl_clob SET clob = :clob WHERE id = :id");
OCI_SetBindAllocation(stmt, OCI_BAM_INTERNAL);
OCI_BindArrayOfLobs(stmt, ":clob", NULL, OCI_CLOB, 0);

string data; // Contains approx. 4 million chars
size_t charCount = data.length();
size_t byteCount = 0;
OCI_LobWrite2(static_cast<OCI_Lob*>(OCI_BindGetData(OCI_GetBind2(stmt, ":clob"))), const_cast<char*>(data.c_str()), &charCount, &byteCount);

... // Bind :id

OCI_Execute(stmt);    // Access Violation during this call

I am using OCILIB 3.9.2 on Oracle 9.2.0.8.

What am I doing wrong?

Regards,
Dries

[Anonymous]

Hi,

I searched the internet and found someone having a similar problem using plain
OCI: https://forums.oracle.com/forums/thread.jspa?threadID=194246 and I read

Either a single locator or an array of locators can be bound in a single
bind call. In each case, the application must pass the address of a LOB
locator and not the locator itself

in the OCI documentation http://download.oracle.com/docs/cd/B13789_01/appdev.
101/b10779/oci05bnd.htm#432118.

So, after some debugging I changed:

            case OCI_CDT_LOB:
            {
                OCI_Lob *lob = OCI_LobCreate(bnd->stmt->con, bnd->subtype);

                if (lob != NULL)
                {
                    bnd->input    = (void **) lob;
                    bnd->buf.data = (void **) lob->handle;
                }

                break;
            }

into

            case OCI_CDT_LOB:
            {
                OCI_Lob *lob = OCI_LobCreate(bnd->stmt->con, bnd->subtype);

                if (lob != NULL)
                {
                    bnd->input    = (void **) lob;
                    bnd->buf.data = (void **) [b]&[/b]lob->handle;
                }

                break;
            }

This fixes the access violation and the data send to database looks ok.

Might this be a bug?

Regards,
Dries

[Vincent Rogier]

Did you set OCI_bindArraySetSize() ??

[Anonymous]

No, I didn't.

If I do, it is working fine. But now another branch is executed in
OCI_BindAllocData and the code, that I changed before, is not executed.

OCI_BindArraySetSize(stmt, 1);
...
OCI_LobWrite2(static_cast<OCI_Lob**>(OCI_BindGetData(OCI_GetBind2(stmt, ":clob")))[0], const_cast<char*>(data.c_str()), &charCount, &byteCount);

[Vincent Rogier]

are you binding an array of lob or just a single lob ?

If you're passing an array, you must use the array interface correctly and use
OCI_BindArraySetSize()

[Anonymous]

I am just binding a single lob.
I (mis)used OCI_BindArrayOfLobs as I could not get OCI_BindLob to do an
internal allocation.

When I do use OCI_BindLob with a given lob, does the statement clean up the
lob or should I call OCI_LobFree?

[Vincent Rogier]

... // Initializing connection

string data;
int id;

... // Initializing DATA AND ID

OCI_Statement* stmt = OCI_StatementCreate(conn);
OCI_Lob * clob = OCI_LobCreate(conn, OCI_CLOB);

OCI_Prepare(stmt, "UPDATE tbl_clob SET clob = :clob WHERE id = :id");

OCI_BindLob(stmt, ":clob", clob);
OCI_BindInt(stmt, ":id", &id);

OCI_LobWrite(clob, const_cast<char*>(data.c_str()), data.length()); </char*>

OCI_Execute(stmt);

[Anonymous]

The database layer am I migrating over from Pro*C is lot more dynamic than the
simple example I gave to demonstrate the problem. Adding the fact
OCI_BAM_INTERNAL and OCI_BindLob can not work together (gives an ORA-24813; it
looks like the OCILobLocator is never assigned to buf.data of the OCI_Bind), I
will use the array interface as you proposed.

Thanks for your help.

As I want use OCI_BAM_INTERNAL f
As I am using OCI_BAM_INTERNAL for the whole

[Vincent Rogier]

OCI_BAM_INTERNAL and OCI_BindLob() should work together.

Do you still have an error if you replace, in the original code you've posted
the call to OCI_BindArrayOfLobs() by OCI_BindLob() ?

[Anonymous]

Replacing it by OCI_BindLob crashes because when called with data == NULL, the
type to use, expected in data->type, is not valid.

[Vincent Rogier]

in fact, OCI_SetBindAllocation() only work for array interface because for
object like lobs, there is no way internally to find out the type of lob to
create (clob or lob)....