FAQ-0531 When is calling HBufC::Des() an error?


FAQ-0531 When is calling HBufC::Des() an error?

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Classification:	C++	Category:	Base
Created:	10/19/2000	Modified:	09/11/2002
Number:	FAQ-0531
Platform:	Not Applicable

Question:
When is calling HBufC::Des() an error?

Answer:
The Des() function is often used incorrectly in EPOC code, most commonly with HBufC's:

// a function that reads from aParam
void foo(const TDesC& aParam);

void foobarL()

{
HBufC* buffer = HBufC::NewL(10); a ten character descriptor.

// ...fill buffer...

foo(buffer->Des()); // call the function that reads from buffer
}

The TBufC<> and HBufC classes provide the member function:

TPtr Des();

to enable you to modify the contents of the memory provided by the descriptor. It should be used whenever a modifiable descriptor type is needed that refers to this memory. Whenever a constant descriptor is needed, observe that both TBufC<> and HBufC derive from TDesC, and can therefore be used directly.

So the example above should be:

// a function that reads from aParam
void foo(const TDesC& aParam);

void foobarL()

{
HBufC* buffer = HBufC::NewL(10); a ten character descriptor.

// ...fill buffer...

foo(*buffer); // call the function that reads from buffer
}