Symbian3/PDK/Source/GUID-A4ECB450-02DA-5E85-91AC-4C8BDE0B9B58.dita
author Dominic Pinkman <Dominic.Pinkman@Nokia.com>
Fri, 22 Jan 2010 18:26:19 +0000
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permissions -rw-r--r--
Addition of the PDK content and example code for Documentation_content according to Feature bug 1607 and bug 1608
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<?xml version="1.0" encoding="utf-8"?>
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<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
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<!-- This component and the accompanying materials are made available under the terms of the License 
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"Eclipse Public License v1.0" which accompanies this distribution, 
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and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
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<!-- Initial Contributors:
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    Nokia Corporation - initial contribution.
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Contributors: 
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-->
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<!DOCTYPE concept
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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
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<concept xml:lang="en" id="GUID-A4ECB450-02DA-5E85-91AC-4C8BDE0B9B58"><title>Writing, Reading and Seeking from a Shared Memory</title><prolog><metadata><keywords/></metadata></prolog><conbody><p>Use the <xref href="GUID-4BABB86A-966A-3535-BD35-568338359825.dita"><apiname>write()</apiname></xref> function to write to shared memory </p> <p>Use the <xref href="GUID-99F32AF6-7248-37B7-901A-76FA23DBCD8A.dita"><apiname>read()</apiname></xref> function to read data from shared memory. </p> <p>Use the <xref href="GUID-84F93A85-9DD3-3D5A-98A7-769E6EDA77D1.dita"><apiname>lseek()</apiname></xref> function to set the file offset associated with a shared memory file descriptor </p> <p>Example: </p> <codeblock id="GUID-60F8E5BB-57F5-5520-A061-43D71436543D" xml:space="preserve">#include &lt;stdio.h&gt;
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#include &lt;sys/mman.h&gt;
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#include &lt;fcntl.h&gt;
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#include &lt;unistd.h&gt;
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#include &lt;errno.h&gt;
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int main(void)
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    {
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    int fd; //File descriptor
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    int ret = 0;
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    if((fd = shm_open("page", O_RDWR|O_CREAT, 0666)) &lt; 0)
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        {
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        printf("Shared memory creation failed with errno %d\n", errno);
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        }
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    else
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        {
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        printf("Shared memory creation was successful\n");
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        }
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    if((ret = write(fd, "symbian", 7)) &lt; 0)
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        {
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        printf("Writing into shared memory failed with errno %d\n", errno);
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        }
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    else
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        {
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        printf("Writing into shared memory was successful\n");
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        }
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    if((ret = lseek(fd, -6, SEEK_END)) &lt; 0)
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        {
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        printf("Seeking from end failed with errno %d\n", errno);
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        }
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    else
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        {
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        printf("lseek was successful\n");
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        }
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    char buf[7];
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    if((ret = read(fd, (void*)buf, 6)) &lt; 0)
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        {
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        printf("Reading from shared memory failed with errno %d\n", errno);
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        }
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    else
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        {
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        printf("Reading from shared memory was successful\n");
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        printf("Buffer read = %s\n", buf);
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        }
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    close(fd);//closing the file descriptor
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    if((ret = shm_unlink("page")) &lt; 0) 
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        {
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        printf("Shared memory unlinking failed with errno %d\n", errno);
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        }
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    else
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        {
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        printf("Shared memory unlinking was successful\n");
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        }
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    return ret;
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    }</codeblock> </conbody><related-links><link href="GUID-9AC6774A-41E9-5298-8696-0A317A09E1E9.dita"><linktext>Librt Overview</linktext> </link> <link href="GUID-BE70DCBF-366A-5054-B0F1-7FCEF45FC735.dita"><linktext>Creating and Unlinking a File
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                Descriptor from a Shared Memory</linktext> </link> <link href="GUID-8F6D6934-8FF0-5045-8AB1-74384BE792EA.dita"><linktext>Retrieving Information about a
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                Shared Memory Object</linktext> </link> <link href="GUID-66402932-5C44-556B-A7AC-1C2D245C8B05.dita"><linktext>Clocks and Timers Tutorial</linktext> </link> </related-links></concept>