Del Ventruella wrote:
Is the corresponding load sequence:
void LoadData(DmOpenRef db, myStructType *myStructP){
MemHandle recH=NULL;
UInt8 *recP;
UInt16 recIndex=-1; //will save the data in a new record at the
end of the database
RecH=DmNewRecord(db, recIndex, sizeof(myStructType));
if (recH){
recP=MemHandleLock(recH);
DmRead(recP,0,myStructP, sizeof(myStructType));
}
}
?
Nope.
You have to FIND the record first, and instead of the DmNewRecord (which
CREATES a new database record) you will probably want to use a
DmQueryRecord() command. When you save the record you will need to tag
it with some kind of identifyer so that you can find it again. You
could put an "id" field in your structure, or you could simply declare
that 2 first bytes of the database record as an identifier (a UInt16
unique number), or you could just keep track of the record index in some
other way (your preferences for the app?)
Once you have found the record you will then access it (DmQueryRecord,
or DmGetRecord). Like so:
MemHandle recH=DmQueryRecord(db, recIndex);
... then read the data. You can read the data directly, by assigning a
pointer, of the same structure type, to the memory location where the
stored data is. Like this:
myStructP=MemHandleLock(recH).
now you can access the saved structure data directly using that pointer.
One other question, the part about saving the pointer data.
The pointer contains the address of the data.
Under PalmOS, there is no hard drive where this data safely resides.
Well, databases are in storage memory, where they are 'safely' stored
unless your battery loses power. Pointers are in dynamic memory, where
they can be easily overwritten, unless you have left them locked..
If the address is overwritten, you lose the data. Okay, that I understand.
How does one store (and load) this pointer data
in a manner that will insure that it is retained?
You would store the pointed-to information in your database, perhaps at
the end of the structure, or as a separate record. There is no
hard-and-fast rule as to how to do this.
I get the impression that what you need to do is to study some of the
example code that is provided with the SDK and tools. These will be
very instructive.
Bob.
--
For information on using the PalmSource Developer Forums, or to unsubscribe,
please see http://www.palmos.com/dev/support/forums/
