Descriptors FAQ

If it needs to be modifiable, use a TBuf. If it's constant, use a TBufC. You'll need to specify the size of stack space allocated for the descriptor's data.

Here’s an example:


_LIT(KFred, “fred”); // A string literal, these will be described later
TBufC<4> constantFred(KFred);

In reality, you probably wouldn't do this for a non-modifiable descriptor, since you can use the literal, KFred directly by calling the operator()() (as I'll describe separately in 22. What are literal descriptors?). That is, instead of creating constantFred, you could just call KFred().

However, this approach is still useful for modifiable descriptors, for example, for logging purposes:

TInt CMyActiveObject::RunError(TInt aError)
{
_LIT8(KError, "CMyActiveObject::RunError: %d");
TBuf8<35> errorBuf;
errorBuf.Format(KError, aError); // reference 3 has more information about TDes::Format()
iLogger.Log(errorBuf); // iLogger is a log object owned by the class
return (KErrNone);
}


What if I want a descriptor to hold ASCII text?

There are some cases where you do need to hold 8-bit text: MIME types, or binary data, for example. To do this, you should explicitly use the 8 bit descriptors:

_LIT8(KImageGif, “image/gif”);
TBufC8<15> mimeType(KImageGif);