<?xml version="1.0" encoding="utf-8"?>

<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

<!-- This component and the accompanying materials are made available under the terms of the License 

"Eclipse Public License v1.0" which accompanies this distribution, 

and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

<!-- Initial Contributors:

    Nokia Corporation - initial contribution.

Contributors: 

-->

<!DOCTYPE concept

  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

<concept id="GUID-261ADCEC-C8C8-46E3-A7DC-804AC868C233" xml:lang="en"><title>Descriptors</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>Descriptors are self-describing strings that can be used to store binary

data and text. Each descriptor object holds the length of the string as well

as its type which identifies the underlying memory layout of the data it holds.

For more information on different descriptor classes, see <xref href="GUID-11EEFB3D-0414-5BEB-9D78-56A4B9154008.dita">Using

Descriptors</xref>.</p>

<p>There are modifiable and non-modifiable descriptors, the latter type

is identified by a "C" suffix in the class name. The length of a non-modifiable

descriptor is defined when compiling an application, and the length of a modifiable

descriptor can vary within the limits set by <codeph>iMaxLength</codeph>.

Nonmodifiable descriptors are more secure, as their length is checked during

compilation. The following figure shows the differences between these types.</p>

<fig id="GUID-A8F9937F-25A6-4E80-845F-35994B7E13E5"><title>Differences between modifiable, nonmodifiable, and pointer descriptors</title><image href="GUID-40619192-8C2F-4267-BFCA-F53E10BF5A31_d0e12841_href.png"/></fig>

<p>When designing applications, avoid using fixed-length buffers as parameters

and use base classes (preferably constant base type <codeph><xref href="jar:GUID-35228542-8C95-4849-A73F-2B4F082F0C44.jar!/sdk/doc_source/reference/reference-cpp/Kernel_Architecture_2/e32cmn.hGlobals.html#%3a%3aTDesC" format="application/java-archive">TDesC</xref></codeph>)

instead. Descriptor objects provide a flexible interface for manipulating

the contained string, including size and length checks. Take advantage of

these when possible.</p>

<p>For more information and examples, see the <xref href="GUID-0817AD1D-58CF-5108-ACBF-26DFD4BA395E.dita">Descriptors

Overview</xref> topic.</p>