>From: Max Bian <[EMAIL PROTECTED]>
>
>This is an interesting programming error. I'd bet the professors would
>love to
>see students making this kind of mistake in CSI 102. J/K :)
>
>After your first call to OpenDB, global variable dbPtr contains the
>reference
>to the first opened database.
>
>When your code calls it the second time, look carefully into the OpenDB
>function, it basically does nothing since dbPtr is not NULL. The old
>reference
>is returned.
>
>To solve this, you can:
>1. set the golbal dbPtr to NULL after you finish with the first database
>2. use a different approach: let OpenDB does only what it supposed to do:
>openning a database. Don't check the dbPtr. It is global! Make your
>calling
>code check the global and take actions accordingly.
>
>Max
Hi Max,
I have set the pointer of the database to NULL.
I went to read the all the records from the database A, set the pointer to
NULL and went to read all the records from database B and set NULL to the
same pointer as well. It works but
When I decide to open the database A again to add all the records to the
database A, I received a NULL value for the databasepointer. Why the pointer
could not point back to the database A again?
Thanks alot...I really need your help as I am been stuck here for a whole
day.
static DmOpenRef OpenDB(Char *DatabaseName)
{
if(dbPtr == NULL)
{
//find database
LocalID dbID = DmFindDatabase( DB_CARDNO , DatabaseName );
if(!dbID)
{ //can't find , create a new database
Err err = DmCreateDatabase( DB_CARDNO , DatabaseName , DB_CREATOR
, DB_TYPE , false );
if(err)
PrintString("got err creating database");
// able to find
dbID = DmFindDatabase( DB_CARDNO, DatabaseName );
if(! dbID)
return NULL;
}
//open the database
dbPtr = DmOpenDatabase( DB_CARDNO , dbID , dmModeReadWrite );
if (dbPtr == NULL)
return NULL;
}
return dbPtr;
}
<<This is my AddRecord()>>
Err AddRecord(Char *DatabaseName,Char *Rec)
{
MemHandle h;
void *ptr;
Err err;
dbPtr = OpenDB(DatabaseName);
if (dbPtr == NULL)
PrintString("dbPtr in the AddRecord return by OpenDB is null");
else
{
Int16 Index = dmMaxRecordIndex; //Get the max record
UInt32 size = StrLen(Rec);
h = DmNewRecord(dbPtr,&Index,size + 1);
if(!h)
return 1;
else
{
ptr = MemHandleLock(h);
DmWrite(ptr, 0 , (Char *) Rec , size + 1 );
MemHandleUnlock(h);
DmReleaseRecord(dbPtr,Index,true);
}
}
return 0;
}
From
Low Pui Kuen
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