Descriptors FAQ

Create an HBufC (or an HBufC8 if you explicitly need 8-bit text).

HBufC* heapbasedFred=HBufC::NewL(4);

But how do I then write to a heap descriptor? HBufC is not derived from a modifiable descriptor class?

This is also easy. First you must call HBufC::Des() to get a TPtr, which is modifiable. You can then use that:

TPtr fredPtr(heapbasedFred->Des());
_LIT(KFred, “fred”);
fredPtr.Copy(KFred);

And how do I read from HBufC?
You can just dereference the HBufC pointer, like this:

TBuf<4> stackbasedFred(*heapBasedFred);

But I’ve seen code which calls Des() on an HBufC. Why’s that?

This is a common mistake, which fortunately does little harm except to overall efficiency.
Des() gives you a modifiable descriptor, TDes, which itself derives from TDesC, so you can use it to call any of the TDesC functions. But it’s unnecessary.

Here’s an example of this common mistake:

TBuf<4> stackbasedFred(heapBasedFred->Des()); // Unnecessary, just use
TBuf<4> stackBasedFred(*heapBasedFred); // More efficient