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

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

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

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

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

needed:</p>

<ul>

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

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

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

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

</ul>

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

defined as:</p>

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

    {

    ...

    TSglQueLink iSlink;

    ...

    };</codeblock>

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

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

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

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

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

list.</p>

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

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

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

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

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

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

<image href="GUID-FB654184-C256-546F-AF6C-E0FADA78D5D0_d0e214615_href.png" placement="inline"/>

</fig>