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    10 <!DOCTYPE concept

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

    12 <concept id="GUID-C85B4EA2-0184-52AF-B097-152E4A023CEF" xml:lang="en"><title>Abstract

    13 base descriptor classes</title><shortdesc>Describes the modifiable descriptor class and the non-modifiable

    14 descriptor class.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    15 <p>The concrete descriptor classes are all derived from a set of base classes.

    16 The base classes are abstract and implement nearly most of the behaviour of

    17 descriptors. They are:</p>

    18 <ul>

    19 <li id="GUID-0942F246-8BB5-50DB-8314-AA4B1DD1B8C0"><p>The abstract non-modifiable

    20 descriptor</p> </li>

    21 <li id="GUID-1750CF5B-E6F3-57E5-A107-B17DA0481E22"><p>The abstract modifiable

    22 descriptor</p> </li>

    23 </ul>

    24 <section id="GUID-136970EE-DFB5-469F-9597-1105AA05947E"><title>The abstract non-modifiable descriptor class</title> <p>The

    25 class has a data member containing the length of the data represented by the

    26 serived concrete descriptor. It also provides the set of functions through

    27 which data can be accessed but not modified.</p> <p>This class is supplied

    28 in two variants:</p> <ul>

    29 <li id="GUID-669B11F1-84DA-5064-88B8-5D3F603114F6"><p>the 16 bit variant,

    30 a <codeph>TDesC16</codeph>, to handle Unicode strings.</p> </li>

    31 <li id="GUID-A9F1113E-0736-570D-BF57-B060817549C8"><p>the 8 bit variant, a <codeph>TDesC8</codeph>,

    32 to handle non-Unicode strings and binary data.</p> </li>

    33 </ul> <p>There is also a build independent type, <codeph>TDesC</codeph>. This

    34 is the type which is most commonly used in program code; the appropriate variant

    35 is selected at build time.</p> <p>An explicit 8 bit variant is chosen when

    36 handling binary data. The explicit 16 bit variant is rarely used.</p> </section>

    37 <section id="GUID-DA165923-2587-4F77-AEAF-FA012B7EAC24"><title>The abstract modifiable descriptor class</title> <p>The class

    38 has a data member containing the maximum length of data that the descriptor

    39 is capable of representing. It also provides the set of functions through

    40 which data can be modified.</p> <p>This class is supplied in two variants:</p> <ul>

    41 <li id="GUID-3F876EFE-1E91-5834-914A-45478D70B0A7"><p>the 16 bit variant,

    42 a <codeph>TDes16</codeph>, to handle Unicode strings.</p> </li>

    43 <li id="GUID-1F1F3894-3CD0-5DEB-AA75-8259CC86BF58"><p>the 8 bit variant, a <codeph>TDes8</codeph>,

    44 to handle non-Unicode strings and binary data.</p> </li>

    45 </ul> <p>There is also a build independent type, <codeph>TDes</codeph>. This

    46 is the type which is most commonly used in program code; the appropriate variant

    47 is selected at build time.</p> <p>An explicit 8 bit variant is chosen when

    48 handling binary data. The explicit 16 bit variant is rarely used.</p> </section>

    49 </conbody></concept>