1 <?xml version="1.0" encoding="utf-8"?>

     2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

     3 <!-- This component and the accompanying materials are made available under the terms of the License 

     4 "Eclipse Public License v1.0" which accompanies this distribution, 

     5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

     6 <!-- Initial Contributors:

     7     Nokia Corporation - initial contribution.

     8 Contributors: 

     9 -->

    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <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;

    13 #include <sys/mman.h>

    14 #include <fcntl.h>

    15 #include <unistd.h>

    16 #include <errno.h>

    17 int main(void)

    18     {

    19     int fd; //File descriptor

    20     int ret = 0;

    21     if((fd = shm_open("page", O_RDWR|O_CREAT, 0666)) < 0)

    22         {

    23         printf("Shared memory creation failed with errno %d\n", errno);

    24         }

    25     else

    26         {

    27         printf("Shared memory creation was successful\n");

    28         }

    29     if((ret = write(fd, "symbian", 7)) < 0)

    30         {

    31         printf("Writing into shared memory failed with errno %d\n", errno);

    32         }

    33     else

    34         {

    35         printf("Writing into shared memory was successful\n");

    36         }

    37     if((ret = lseek(fd, -6, SEEK_END)) < 0)

    38         {

    39         printf("Seeking from end failed with errno %d\n", errno);

    40         }

    41     else

    42         {

    43         printf("lseek was successful\n");

    44         }

    45     char buf[7];

    46     if((ret = read(fd, (void*)buf, 6)) < 0)

    47         {

    48         printf("Reading from shared memory failed with errno %d\n", errno);

    49         }

    50     else

    51         {

    52         printf("Reading from shared memory was successful\n");

    53         printf("Buffer read = %s\n", buf);

    54         }

    55     close(fd);//closing the file descriptor

    56     if((ret = shm_unlink("page")) < 0) 

    57         {

    58         printf("Shared memory unlinking failed with errno %d\n", errno);

    59         }

    60     else

    61         {

    62         printf("Shared memory unlinking was successful\n");

    63         }

    64     return ret;

    65     }</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

    66                 Descriptor from a Shared Memory</linktext> </link> <link href="GUID-8F6D6934-8FF0-5045-8AB1-74384BE792EA.dita"><linktext>Retrieving Information about a

    67                 Shared Memory Object</linktext> </link> <link href="GUID-66402932-5C44-556B-A7AC-1C2D245C8B05.dita"><linktext>Clocks and Timers Tutorial</linktext> </link> </related-links></concept>