<?xml version="1.0" encoding="utf-8"?>+
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<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->+
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<!-- Initial Contributors:+
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    Nokia Corporation - initial contribution.+
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Contributors: +
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<!DOCTYPE concept+
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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">+
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<concept id="GUID-4F2F254A-1A81-507A-B364-BE4088D3B3AE" xml:lang="en"><title>How to+
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use literal descriptors</title><shortdesc>Explains how to generate constant literal descriptors.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>+
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<p>Generate a constant literal as follows:</p>+
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<codeblock id="GUID-C3147B10-3247-5EC8-8ED9-A9574EEE4682" xml:space="preserve">_LIT(name, string);</codeblock>+
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<p>where <codeph>name</codeph> is a C++ variable name and <codeph>string</codeph> is+
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the literal text enclosed in a pair of double quotes. </p>+
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<p>All the code fragments use the build independent form but they are equally+
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valid if replaced by the explicit 16 bit variant or the explicit 8 bit variant.</p>+
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<p>As <codeph>name</codeph> represents a constant variable, it is conventional+
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for the variable name to start with a capital <codeph>K</codeph>, for example:</p>+
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<codeblock id="GUID-9CA8C2BA-403B-5E43-A205-0C5690872988" xml:space="preserve">_LIT(KTxtMatchString,"Hello");</codeblock>+
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<p>This generates the constant literal descriptor:</p>+
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<codeblock id="GUID-B40B7B03-CD17-509B-86A2-701D3A902A9A" xml:space="preserve">const static TLitC&lt;5&gt; KTxtMatchString;</codeblock>+
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<p>and this is initialised to contain the string <codeph>Hello</codeph>. Developers+
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never need to code a <codeph>TLitC</codeph> class explicitly; it is always+
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be constructed through the macro.</p>+
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<p>This constant literal descriptor can be passed directly to functions which+
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are prototyped to take a <codeph>const TDesC&amp;</codeph> type:</p>+
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<codeblock id="GUID-CEAF3352-ED10-5E05-9571-F032375FFEE6" xml:space="preserve">TBufC&lt;32&gt; x;+
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...+
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x.Match(KTxtMatchString);+
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...</codeblock>+
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<p>The literal descriptor classes: <codeph>TLitC16</codeph>, <codeph>TLitC8</codeph>, <codeph>TLitC16</codeph>,+
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also provide a conversion operator so that they can be passed to functions+
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which take a <codeph>const         TRefByValue&lt;const TDesC&gt;</codeph> type.+
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This means that they can be passed to functions such as <codeph>TDes::Format()</codeph>:</p>+
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<codeblock id="GUID-0D9639D7-B7EE-50E1-B21A-09D8C0D0FF0A" xml:space="preserve">_LIT(KFormat1,"Length is %d");+
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...+
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TBuf&lt;256&gt; x;+
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...+
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x.Format(KFormat1,8);+
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...</codeblock>+
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<p>The <codeph>&amp;</codeph> and the <codeph>()</codeph> operators acting+
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on a constant literal return a <codeph>const TDesC*</codeph> and a <codeph>const+
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        TDesC&amp;</codeph> type respectively:</p>+
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<codeblock id="GUID-4DA3E378-B0EA-5336-A921-282C632795CC" xml:space="preserve">...+
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_LIT(KTxtMatchString,"Hello");+
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_LIT(KFormat2,"Text is %S");+
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...</codeblock>+
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<codeblock id="GUID-B83E52DD-2638-57EE-BA80-B9377C40404A" xml:space="preserve">TInt length;+
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length = KTxtMatchString().Length();+
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...+
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TBuf&lt;256&gt; x;+
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x.Format(KFormat2,&amp;KTxtMatchString);+
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...</codeblock>+
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</conbody></concept>+
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