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<concept id="GUID-4F2F254A-1A81-507A-B364-BE4088D3B3AE" xml:lang="en"><title>How to

use literal descriptors</title><shortdesc>Explains how to generate constant literal descriptors.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>Generate a constant literal as follows:</p>

<codeblock id="GUID-C3147B10-3247-5EC8-8ED9-A9574EEE4682" xml:space="preserve">_LIT(name, string);</codeblock>

<p>where <codeph>name</codeph> is a C++ variable name and <codeph>string</codeph> is

the literal text enclosed in a pair of double quotes. </p>

<p>All the code fragments use the build independent form but they are equally

valid if replaced by the explicit 16 bit variant or the explicit 8 bit variant.</p>

<p>As <codeph>name</codeph> represents a constant variable, it is conventional

for the variable name to start with a capital <codeph>K</codeph>, for example:</p>

<codeblock id="GUID-9CA8C2BA-403B-5E43-A205-0C5690872988" xml:space="preserve">_LIT(KTxtMatchString,"Hello");</codeblock>

<p>This generates the constant literal descriptor:</p>

<codeblock id="GUID-B40B7B03-CD17-509B-86A2-701D3A902A9A" xml:space="preserve">const static TLitC&lt;5&gt; KTxtMatchString;</codeblock>

<p>and this is initialised to contain the string <codeph>Hello</codeph>. Developers

never need to code a <codeph>TLitC</codeph> class explicitly; it is always

be constructed through the macro.</p>

<p>This constant literal descriptor can be passed directly to functions which

are prototyped to take a <codeph>const TDesC&amp;</codeph> type:</p>

<codeblock id="GUID-CEAF3352-ED10-5E05-9571-F032375FFEE6" xml:space="preserve">TBufC&lt;32&gt; x;

...

x.Match(KTxtMatchString);

...</codeblock>

<p>The literal descriptor classes: <codeph>TLitC16</codeph>, <codeph>TLitC8</codeph>, <codeph>TLitC16</codeph>,

also provide a conversion operator so that they can be passed to functions

which take a <codeph>const         TRefByValue&lt;const TDesC&gt;</codeph> type.

This means that they can be passed to functions such as <codeph>TDes::Format()</codeph>:</p>

<codeblock id="GUID-0D9639D7-B7EE-50E1-B21A-09D8C0D0FF0A" xml:space="preserve">_LIT(KFormat1,"Length is %d");

...

TBuf<256> x;

...

x.Format(KFormat1,8);

...</codeblock>

<p>The <codeph>&amp;</codeph> and the <codeph>()</codeph> operators acting

on a constant literal return a <codeph>const TDesC*</codeph> and a <codeph>const

        TDesC&amp;</codeph> type respectively:</p>

<codeblock id="GUID-4DA3E378-B0EA-5336-A921-282C632795CC" xml:space="preserve">...

_LIT(KTxtMatchString,"Hello");

_LIT(KFormat2,"Text is %S");

...</codeblock>

<codeblock id="GUID-B83E52DD-2638-57EE-BA80-B9377C40404A" xml:space="preserve">TInt length;

length = KTxtMatchString().Length();

...

TBuf<256> x;

x.Format(KFormat2,&KTxtMatchString);

...</codeblock>

</conbody></concept>