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    10 <!DOCTYPE concept

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

    12 <concept id="GUID-7830BAAB-40DD-5E55-84B5-8DCA888E68E7" xml:lang="en"><title>Using

    13 TDesC</title><shortdesc>Use TDesC for interfaces which take narrow or wide (Unicode) text,

    14 depending on the build variant, but does not change the data.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    15 <section id="GUID-235E272D-6F5A-5740-8150-9698C8C8D55D"><title>Usage in a

    16 function interface</title> <p>An interface which needs access to either narrow

    17 text or wide (Unicode) text, depending on the build variant, but which does

    18 not need to change that data in any way, can use a <xref href="GUID-52D07F46-2162-380C-A775-C3BB335C42F5.dita"><apiname>TDesC</apiname></xref> as

    19 the argument type. All build independent concrete descriptors are derived

    20 from <codeph>TDesC</codeph> which means that the interface can accept any

    21 build independent descriptor.</p> <p>The following code fragment shows the

    22 most common function prototype pattern.</p> <codeblock id="GUID-1FAB92F0-D8D1-51C9-B993-9F0FF93659B3" xml:space="preserve">void ClassX::foo(const TDesC&amp; anArg);</codeblock> <p>The use of <codeph>TDesC</codeph> ensures that the data cannot be modified

    23 through the descriptor; <codeph>const</codeph> is an extra guarantee that

    24 the data cannot be changed.</p> <p>If the interface is to handle explicit

    25 8 bit or explicit 16 bit data, regardless of the build variant, then use <codeph>TDesC8</codeph> or <codeph>TDesC16</codeph> instead.</p> </section>

    26 </conbody></concept>