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

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     7     Nokia Corporation - initial contribution.

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    10 <!DOCTYPE concept

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

    12 <concept id="GUID-7572B1F0-66CD-53B8-A479-4A078C9CB28A" xml:lang="en"><title>Module

    13 definition file</title><shortdesc>Module definition file contains the list of exported functions

    14 of a Polymorphic DLL.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    15 <p>In conventional systems, DLLs may export by name or by ordinal. Symbian

    16 platform only supports exporting by ordinal. Exporting by ordinal reduces

    17 the time taken to find the item in the DLL export table and also reduces the

    18 size of the DLL as names need not be stored. Ordinals are used for accessing

    19 the address of a function in the <keyword>DLL export table</keyword>.</p>

    20 <p>The only item which should be exported from a polymorphic interface DLL

    21 is a function which returns an instance of the object supplied by the DLL;

    22 this should be exported at ordinal 1.</p>

    23 <p>Once a user program has created an instance of the object supplied by the

    24 DLL, other DLL functions may be accessed using the virtual function table;

    25 such functions do not need to be exported.</p>

    26 <p>A <keyword>module definition file</keyword> (<filepath>.def</filepath>)

    27 is a text file which lists the <keyword>exported</keyword> functions of a

    28 DLL; it is used in an <keyword>ordinal build</keyword> to insert ordinal information

    29 into the DLL export table.</p>

    30 <p>It is only necessary to create this file for a polymorphic interface DLL;

    31 static interface DLLs use an <keyword>import library</keyword> to obtain relevant

    32 information about exported functions.</p>

    33 </conbody></concept>