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<concept id="GUID-D69DD425-5F93-4238-A7E9-915F24A9C9CA" xml:lang="en"><title>Open

C MessageQueue Library Example</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>The Message Queue Library example demonstrates how to use Open C APIs for

developing applications that use Open C standard libraries on Symbian platform.

This example uses the APIs of the message queue library to create/close message

queues and send/receive messages and also get information on created message

queues. </p>

<section id="GUID-026FD8D6-6C4A-5958-B289-775D4AE1E756-GENID-1-10-1-11-1-1-5-1-3-1-11-1-12-1-2-2"><title>Download</title> <p>Click

on the following link to download the example: <xref href="guid-6013a680-57f9-415b-8851-c4fa63356636/zips/guid-9db026cc-ac23-4593-8bbc-4b251c085d4f.zip" scope="external"> opencmessagequeuelibraryex.zip</xref></p><p>Click: <xref href="guid-6013a680-57f9-415b-8851-c4fa63356636/guid-9db026cc-ac23-4593-8bbc-4b251c085d4f.html" scope="peer">browse</xref> to view the example code. </p> </section>

<section id="GUID-7E7C4564-B10E-41F9-8A9D-D8A6C5E9C51C-GENID-1-10-1-11-1-1-5-1-3-1-11-1-12-1-2-3"><title>Design and

Implementation</title> <p>The following sections provide information about

the implementation of the example. </p><p><b>Description</b></p><p>OpenCMessageQueueClientEx

is a C Application that uses the  Message Queue library. This application

uses main() as the entry point for the application. This is a simple console

based application. The application uses Message Queue library (OpenCMessageQueueLibrary.dll)

APIs.  The Main thread of the application creates two message queues, and

two threads. Thread one will send message to message queue 1 and waits for

messages from message queue 2. Then thread one will send message to message

queue 2 and waits for messages from message queue 1. If a user tries to create

a message queue using OpenCMessageQueueLibrary.dll with the already

existing name, it will just return the existing message queue Id. The application

has its own icon and can be launched from the UI both in the emulator  and

in the device. </p><p><b>Capabilities</b> </p> The program capabilities are

defined in:  <filepath>MessageQueueLibrary.mmp</filepath> (DLL - library):<codeph> CAPABILITY

ALL -TCB</codeph> <filepath>MessageQueueClient.mmp</filepath>(EXE - application): <codeph>CAPABILITY

NONE</codeph>. <p><b>Module hierarchy</b> </p>This application has 2 modules

as below:  <p>Message Queue Library (DLL) that exports set of apis for the

user.</p><p>OpenCMessageQueueLibraryEx\engine : The application (EXE) that

demonstrates the usage of Open C APIs and also those APIs exported by Message

Queue Library.</p><p> (OpenCMessageQueueLibraryEx\exe) : This example will

create a DLL which exports set of generic APIs with which the user can do

message queue related operations.   To give a rough idea on how to use these

apis, an EXE is provided that creates threads and does send/receive on message

queues using those exported apis.</p><p><b>APIs used</b></p><p>msgget </p><p> msgctl

 </p><p>msgrcv  </p><p>msgsnd  </p><p>semget  </p><p>semctl </p><p> semop </p> </section>

<section id="GUID-67A72761-1D92-46D1-B1C9-7455978BDE4E-GENID-1-10-1-11-1-1-5-1-3-1-11-1-12-1-2-4"><title>Building and

Using</title> To build the Message Queue Library example application, go to

the <filepath>OpenCMessageQueueLibraryEx\group</filepath> directory and build

the application.  The Message Queue Library application consists of two modules,

which should be built in the following order:   engine - which builds the

generic message queue library  exe - which builds an EXE that demonstrates

the usage of this library  The definition for the whole application can be

found in the<filepath>bld.inf</filepath>in the group subdirectory of the applications

main directory. </section>