passing OCI_Connection * to a function

[Nobody/Anonymous]

Hi Vincent.

I craeted a function called Connect2DB()
its prototype is: extern int Connect2DB(OCI_Connection cn, OCI_Statement st, OCI_Error *err);
I call this function using Connect2DB(cn,st,err)
Inside the function cn gets a value, but when returning to the caller program cn equals NULL.

when I Run the program

-

OCI_Error err = NULL;
OCI_Connection cn = NULL;
OCI_Statement *st = NULL;

printf("Return Status is: %d\n",Connect2DB(cn,st,err));
if (cn == NULL) printf("cn After returning from Connect2DB() is NULL\n");

This is the function:

extern int Connect2DB(OCI_Connection cn, OCI_Statement st, OCI_Error err)
{
OCI_Connection cn1;

cn = OCI_ConnectionCreate("XE","system","manager",OCI_SESSION_DEFAULT);
if (cn == NULL) printf("cn is NULL\n");
else puts("cn inside Connect2DB() is not NULL");
if (!cn) return(False);
st = OCI_StatementCreate(cn);
return(True);

}

I get

-

cn inside Connect2DB() is not NULL
Return Status is: 1
cn After returning from Connect2DB() is NULL

cn is a pointer, so it should hold the address to a OCI_Connection struct after returning from Connect2DB()
but is holds NULL instead.
Any idea why?
Thanks,

Gillian

[Nobody/Anonymous]

Hi,
Sorry for misunderstanding,
Now it looks like this.

if (!OCI_Initialize(ErrorHandling,NULL,OCI_ENV_DEFAULT)) return(False);

[Vincent Rogier]

Hi,

In fact, it's normal that when your function returns, the value of cn is NULL.

Because the C language only knows one way to pass parameters : by value.

It means that it's a copy of the pointer 'cn' that is used inside the your function...

Your orignal pointer is not modified !! Same for 'st' !

What you should do is to pass the address of your pointers 'cn' and 'st'.

Like :

extern int Connect2DB(OCI_Connection cn, OCI_Statement st, OCI_Error *err);

And call it as :

Connect2DB(&cn,&st,&err);

Why do you pass an OCI_Error pointer ?

Vincent

[Nobody/Anonymous]

Hi,

Thanks it works.

The reason I do that is because I want OCILIB to be transparent to the top level program/programers
Take a look at this code, it works.

Top level Program:
/ ------------------------------------------------------------------------ *
* prototypes
* ------------------------------------------------------------------------ /

extern int SelectFromTable(void st, void verr);
extern int InitConnection(void verr);
extern int Connect2DB(void cn, void st, void err);
extern void err_handler(void err, short ExitFlg);
extern void print_version(void vcn);
extern void DisconnectDB(void cn);

-

int mtmain()
{
void verr, vcn, *vst;

if (!InitConnection(&verr)) err_handler(verr,True);
if (!Connect2DB(&vcn,&vst,&verr)) err_handler(verr,True);
print_version(vcn);
if (!SelectFromTable(vst,&verr)) err_handler(verr,False);
DisconnectDB(vcn);
CleanAll();
return EXIT_SUCCESS;

}

InitConnection Dunction:

extern int InitConnection(void *verr)
{
OCI_Error err = NULL;

err = (OCI_Error ) verr;

if (!OCI_Initialize(NULL,NULL,OCI_ENV_DEFAULT)) return(False);
*verr = err;
return(True);

}

Connect2DB function:

extern int Connect2DB(void vcn, void vst, OCI_Error err)
{
OCI_Connection cn;
OCI_Statement *st = NULL;

cn = OCI_ConnectionCreate("XE","system","manager",OCI_SESSION_DEFAULT);
 if (cn == NULL) printf("cn is NULL\n");
if (!(cn)) return(False);

st = OCI_StatementCreate(cn);
vcn = (OCI_Connection ) cn;
vst = (OCI_Statement ) st;
return(True);
}

SelectFromTable Function:

extern int SelectFromTable(OCI_Statement st, OCI_Error err)
{
OCI_Resultset *rs = NULL;

if (!OCI_ExecuteStmt(st, MT("SELECT name,age FROM persons"))) return(False);
rs = OCI_GetResultset(st);
while (OCI_FetchNext(rs))
{
    print_frmt("Name: %s",OCI_GetString(rs, 1));
    print_frmt(" Age : %i", OCI_GetInt(rs,2));
    print_text("\n");

}
print_frmt("count : %i\n", OCI_GetRowCount(rs));
return(True);
}

err_handler Function:

extern void err_handler(OCI_Error *err, short ExitFlg)
{
print_text("\n");

if (OCI_ErrorGetType(err) == OCI_ERR_API)
{
    const mtext *sql = OCI_GetSql(OCI_ErrorGetStatement(err));

    if (sql != NULL)
    {
        print_text("> ERROR - SQL : "); print_mstr(sql);
        print_text("\n");
    }
}

print_text("> ERROR - MSG : ");
print_mstr(OCI_ErrorGetString(err));
print_text("\n");
nb_err++;
if (ExitFlg) exit(0);

}

DisconnectDB Function:

extern void DisconnectDB(void vcn)
{
OCI_Connection cn = NULL;

cn = (OCI_Connection *) vcn;
printf("Disconnecting ...\n");
OCI_ConnectionFree(cn);

}
As you can see, in the top level program, OCILIB is not declared, and the program is indifferent to OCI.

Gillian

[Vincent Rogier]

Hi Gillian,

You're not using the void *err parameter in your functions..

Anyway ,the only way to get an OCI_Error handle is inside the error handler callback that you cna supply to OCI_Initialize().

And the OCI_Error handle passed to the callback is avaible only inside the callback. When the callback returns, the error handler is destroyed !

The mechanisms you're using for error handling cannot work...

[Nobody/Anonymous]

Hi
Have another question,

When I run the program from command line (cmd.exe) it works,
but when I run it from application console (Pelles C interface), it failes right on the first function - InitConnection()
Any ideas?

Gillian

[Vincent Rogier]

See my previous answer...

[Nobody/Anonymous]

Sorry I copied the old version of err_handler()
Now It looks like this:

include <stdio.h>

include <stdlib.h>

include "DBHandle_literals.h"

include "GlobalDef.h"

/ ------------------------------------------------------------------------ *
* prototypes
* ------------------------------------------------------------------------ /
extern int SelectFromTable(void st, void verr, char SQLCmd);
extern int InitConnection(void verr);
extern int Connect2DB(void vcn, void vst, void verr,char DBName, char UserName, char Password);
extern void ErrorHandling(void verr, short ExitFlg);
extern void print_version(void vcn);
extern void DisconnectDB(void vcn);
extern void CleanAll(void);

static char DBName = "XE", UserName = "system", Password = "manager";
static char SQLCmd = "SELECT name,age FROM persons";

/ ------------------------------------------------------------------------ *
* main
* ------------------------------------------------------------------------ /

int main()
{
void verr, vcn, *vst;

if (!InitConnection(&verr)) ErrorHandling(verr,True);
if (!Connect2DB(&vcn,&vst,&verr,DBName,UserName,Password)) ErrorHandling(verr,True);
print_version(vcn);
if (!SelectFromTable(vst,&verr,SQLCmd)) ErrorHandling(verr,False);
DisconnectDB(vcn);
CleanAll();

printf("\npress any key to exit...");
getchar();

return True;

}

extern void ErrorHandling(void verr, short ExitFlg)
{
OCI_Error err = NULL;

err = (OCI_Error *) verr;

if (OCI_ErrorGetType(err) == OCI_ERR_API)
{
    const mtext *sql = OCI_GetSql(OCI_ErrorGetStatement(err));

    if (sql != NULL)
    {
        print_text("> ERROR - SQL : "); print_mstr(sql);
        print_text("\n");
    }
}

print_text("> ERROR - MSG : ");
print_mstr(OCI_ErrorGetString(err));
print_text("\n");
nb_err++;
if (ExitFlg) exit(0);

}

What about the last question I asked?

[Vincent Rogier]

As i said, an OCI_Error handle "lives" the time of the callback.

If you get back the handle ouside the callback, it will point to already freed memory and leads to a segfault.

For your last question, is the ocilib dll accessible to your program ? Check the path, the location where you put the dll, ...

Your actual error handing will fail at the first error raised by ocilib.
Start by change it first...

[Nobody/Anonymous]

Hi Vincent, Is this a better error handling?
The error handling is within the function.

-

Call to InitConnection()

-

InitConnection Function:

extern void ErrorHandling(OCI_Error *err, short ExitFlg);

extern int InitConnection()
{
OCI_Error *err = NULL;

if (!OCI_Initialize(NULL,NULL,OCI_ENV_DEFAULT))
   {
     ErrorHandling(err,True);
 return(False);
};
return(True);

}

ErrorHandling Function:

extern void ErrorHandling(OCI_Error err, short ExitFlg)
{
if (OCI_ErrorGetType(err) == OCI_ERR_API)
{
const mtext sql = OCI_GetSql(OCI_ErrorGetStatement(err));

    if (sql != NULL)
    {
        print_text("> ERROR - SQL : "); print_mstr(sql);
        print_text("\n");
    }
}

print_text("> ERROR - MSG : ");
print_mstr(OCI_ErrorGetString(err));
print_text("\n");
if (ExitFlg) exit(0);

}

[Vincent Rogier]

Once again, you haven't supplied an error handler to OCI_Initiliaze(). If you do not, you'll never retreive an error handle !!!!

Take two minutes to look at your own code : in InitConnection(), you're calling ErrorHandling() with a NULL OCi_Error handle...

What you should do :

1 - Supply to OCI_Initialize() an error handle (the prototype is in the documentation)
2 - When an error occurs, you can retreive the error attributes, locally in the handler
3 - Ouput the error attributes from inside the handler
4 - if you really want to raise those attributes outside the handler, wnat you can do is
A - create your own error structure
B - declare a static error structure variable
C - copy the OCI_Error handle attributes to your own structure
D - is a OCILIB function returns FALSE, you can use your static variable to access the error attributes

Vincent.