Chapter 1

� Without the aLength parameter, the whole descriptor is written.
� The const TUint8* variant writes aLength bytes from the pointer specified.
� The const TDesC16 and const TUint16* variants write Unicode characters (with
little-endian byte order) instead of bytes.
RReadStream comes with similar (though not precisely symmetrical) functions:
class RReadStream
{
public:
//
...
IMPORT_C void ReadL(TDes8& aDes);
IMPORT_C void ReadL(TDes8& aDes, TInt aLength);
IMPORT_C void ReadL(TDes8& aDes, TChar aDelim);
IMPORT_C void ReadL(TUint8* aPtr, TInt aLength);
IMPORT_C void ReadL(TInt aLength);
...
IMPORT_C void ReadL(TDes16& aDes);
IMPORT_C void ReadL(TDes16& aDes, TInt aLength);
IMPORT_C void ReadL(TDes16& aDes, TChar aDelim);
IMPORT_C void ReadL(TUint16* aPtr, TInt aLength);
...
The problem when reading is to know when to stop. When you're writing, the descriptor
length (or the aLength parameter) specifies the data length. When you're reading, the rules
work like this:
� The TDes8& aDes format passes a descriptor whose MaxLength()bytes will be
read.
� If you specify aLength explicitly, then that number of bytes will be read.
� If you specify a delimiter character, the stream will read up to and including that
character. If the MaxLength() of the target descriptor is encountered before the
delimiter character, reading stops after MaxLength() characters – nothing is read and
thrown away.
Like all other ReadXxxL() functions, these functions will leave with KErrEof (end of file) if
the end of file is encountered during the read operation.
You should use these raw data functions with great care. Any data that you externalize with
WriteL() is effectively struct-dumped into the stream. This is fine provided that the data is
already in external format. Be sure that it is!
When you internalize with ReadL(), you must always have a strategy for dealing with the
anticipated maximum length of data. For example, you could decide that it would be
unreasonable to have more than 10 000 bytes in a particular string and so you check the
length purportedly given and if you find it's more than 10 000 you leave with KErrCorrupt.
That's what HBufC::AllocL(RReadStream&,TInt) does.
Strings