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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="GUID-D1C5BB01-6780-41D6-B47B-43D4C983B0B6" xml:lang="en"><title>API
Export</title><shortdesc>This document discusses how to export a device driver API.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>A driver can export its API to be used by other Kernel code by using <codeph>EXPORT_C</codeph> in
the declaration and <codeph>IMPORT_C</codeph> in the definition. When the
driver is built, these functions are exported to a <filepath>.def</filepath> file.
The <filepath>.def</filepath> file is specific to the platform to which the
driver is built. </p>
<codeblock id="GUID-3E732A29-D285-5A51-AF25-9B4B06049632" xml:space="preserve">// Kernel extension internal API
class DExController: public DBase
    {
    …
    void MyExAPI();
    …
    };

// Client interface API
class TExClientInterface
    {
    …
    // static function being exported, this API will go into def file 
    // generated while building
    IMPORT_C static void MyExAPI();
    …
    };

// Global instance of the object
DExController *ExController = NULL; 

// Implementation of the kernel extension's exported function
EXPORT_C void TExClientInterface::MyExAPI()
    {
    …
    ExController-&gt;MyExAPI();
    …
    }</codeblock>
<p>Kernel extensions can also provide information to user programs by setting
attributes that can be read through the system HAL (Hardware Abstration Layer)
API. See<xref href="GUID-124AC7EE-E227-5358-A755-628FFE257250.dita"> Handler Implementation</xref> for
more information on this. </p>
</conbody></concept>