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

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    10 <!DOCTYPE concept

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

    12 <concept id="GUID-59ED6D14-0976-58AE-8DDC-73F051866406" xml:lang="en"><title>How

    13 to construct a header</title><shortdesc>The header of a linked list needs to know the type of data for

    14 each list element, and where in each element the pointer to the next element

    15 can be found.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    16 <p>In order to construct a header, two important pieces of information are

    17 needed:</p>

    18 <ul>

    19 <li id="GUID-5BD8E773-5793-5C52-BF07-62FF1839F19A"><p>the <i>type</i> of object

    20 which forms the elements.</p> </li>

    21 <li id="GUID-9E43534B-D692-53CE-83D9-FE4F1B2DFC42"><p>the <i>offset</i> of

    22 the link object from the start of the element.</p> </li>

    23 </ul>

    24 <p>To create a header for a singly linked list of <codeph>CMyClass</codeph> elements,

    25 defined as:</p>

    26 <codeblock id="GUID-8851C435-33CD-5F1C-95E3-60CEC2770D64" xml:space="preserve">class CMyClass : public CBase

    27     {

    28     ...

    29     TSglQueLink iSlink;

    30     ...

    31     };</codeblock>

    32 <p>construct a <codeph>TSglQue</codeph> as follows:</p>

    33 <codeblock id="GUID-D634E7AB-9240-5F0E-9D36-BE476B038842" xml:space="preserve">TSglQue&lt;CMyClass&gt; queHeader(_FOFF(CMyClass,iSlink));</codeblock>

    34 <p>The <codeph>TSglQue</codeph> class takes a class template parameter which

    35 defines the type of object which is to form an element of the list. In this

    36 example, objects of type <codeph>CMyClass</codeph> form the elements of the

    37 list.</p>

    38 <p>The <codeph>_FOFF</codeph> macro (i.e. the "field offset" macro) calculates

    39 the offset of the component link object within the element. In this example,

    40 the required value is the offset of the <codeph>iSlink</codeph> data member

    41 from the start of <codeph>CMyClass</codeph>. </p>

    42 <fig id="GUID-3B9C78A4-02FC-5D63-AFD2-53996F9CAEC7">

    43 <title>Links in singly linked lists</title>

    44 <image href="GUID-FB654184-C256-546F-AF6C-E0FADA78D5D0_d0e218352_href.png" placement="inline"/>

    45 </fig>

    46 </conbody></concept>