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<concept id="GUID-579D7C32-B6C8-5C77-88A5-B3078729E1BA" xml:lang="en"><title>How

to implement a simple client interface</title><shortdesc>Provides code snippets to help you to implement a simple client

interface.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<section id="GUID-EE1BFD0F-EE55-47BA-A8FD-D753EC132255"><title>Client side session with a server</title> <p>A client side

session is represented by an instance of a class derived from <codeph>RSessionBase</codeph> which

provides the behaviour for connecting to the server and sending messages to

it. </p> <p>In the following code fragment, taken from the example that can

be found at <filepath>...\examples\Base\IPC\ClientServer\simple</filepath>,

the class <codeph>RCountServSession</codeph>, derived from <codeph>RSessionBase</codeph>,

represents the client side session with a server. In the example, this may

be referred to as the "count server". Note that sessions can not be shared

in this example, and it just shows the basic mechanics of the client/server

interaction. </p> <codeblock id="GUID-48AC1BF2-BA67-5959-A49A-AF57AC25E155" xml:space="preserve">class RCountServSession : public RSessionBase

    {

public:

    RCountServSession();

    TInt Connect();

    TVersion Version() const;

    TInt UnsupportedRequest();

    TInt SetFromString(const TDesC& aString);

    void Increase();

    void Decrease();

    void IncreaseBy(TInt anInt);

    void DecreaseBy(TInt anInt);

    void Reset();

    TInt CounterValue();

    void BadRequest();

    void Close();

private:

    RThread iServerThread;

    };</codeblock> <p>The important points are: </p> <ul>

<li id="GUID-B6AC51AC-91A3-5794-815A-292E308735F6"><p>Use <codeph>Connect()</codeph> to

start the count server. This calls <codeph>RSessionBase::CreateSession()</codeph> to

create a session with the server. Note that in this simple example, the server

is implemented as a separate thread, which is started by the example executable. </p> </li>

<li id="GUID-EBDC7F23-8D2F-5093-8C32-50C3DE137EF5"><p>Use a client interface

function, such as <codeph>Increase()</codeph>, to send a specific message

to the server. The client interface function builds the message using the

appropriate operation code and assembling a suitable <xref href="GUID-4AD02F14-1142-372F-9D11-224595932034.dita"><apiname>TIpcArgs</apiname></xref> object,

i.e. the object containing the integers and/or the descriptor pointers to

the message arguments in the client address space. </p> </li>

</ul> <p>As an example, the function <codeph>SetFromString()</codeph> is implemented

as follows: </p> <codeblock id="GUID-A673A2A4-0999-5EDE-9FFB-E0C7335B58D9" xml:space="preserve">TInt RCountServSession::SetFromString(const TDesC&amp; aString)

    {

    TIpcArgs args(&aString);

    return SendReceive(ECountServSetFromString, args);

    }</codeblock> <p> <codeph>SendReceive()</codeph> is called, specifying

an operation code <codeph>ECountServSetFromString</codeph> and a <xref href="GUID-4AD02F14-1142-372F-9D11-224595932034.dita"><apiname>TIpcArgs</apiname></xref> object

containing argument values. In this case, there is only one argument - a pointer

to a <codeph>TDesC</codeph> object containing the string to be passed to the

server. Typically, operation codes are enum values defined in a header file

visible to both the client interface and the server. Note that the client

descriptor must remain in existence until the server request completes. </p> </section>