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1 <?xml version="1.0" encoding="utf-8"?> |
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2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. --> |
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3 <!-- This component and the accompanying materials are made available under the terms of the License |
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4 "Eclipse Public License v1.0" which accompanies this distribution, |
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5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". --> |
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6 <!-- Initial Contributors: |
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7 Nokia Corporation - initial contribution. |
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8 Contributors: |
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9 --> |
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10 <!DOCTYPE task |
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11 PUBLIC "-//OASIS//DTD DITA Task//EN" "task.dtd"> |
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12 <task id="GUID-A7C26FE4-54B2-58D6-9FDF-4B0A565D00DE" xml:lang="en"><title>Seeking |
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13 a Position in a Large File </title><shortdesc>This tutorial shows how to seek a particular position in a large |
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14 file. </shortdesc><prolog><metadata><keywords/></metadata></prolog><taskbody> |
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15 <context><p>The function <xref href="GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7.dita#GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7/GUID-58F3EDD5-7DEF-38AA-A9B6-B68782B3FE83"><apiname>RFile64::Seek()</apiname></xref> is the 64-bit |
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16 version of <xref href="GUID-BE0804F6-4375-3C8A-8C83-968F510466E0.dita#GUID-BE0804F6-4375-3C8A-8C83-968F510466E0/GUID-07136402-8D95-3256-9591-EE4141748E15"><apiname>RFile::Seek()</apiname></xref>. The <codeph>Seek()</codeph> function |
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17 can modify the file pointer to point to any position addressable by the <codeph>aPos</codeph> parameter. </p> <p> <xref href="GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7.dita#GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7/GUID-C4E483DB-4292-3619-95F3-87F70AC6EB19"><apiname>RFile64::Seek(TSeek |
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18 aMode, TInt64& aPos)</apiname></xref>. </p> <p>To get the current position of |
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19 the file pointer use the <xref href="GUID-CA98DC2A-4B7D-336D-A251-C29120DDD444.dita"><apiname>TSeek</apiname></xref> mode <xref href="GUID-054ECFC9-C8C2-32B6-81DE-0526B3B17FF1.dita"><apiname>ESeekCurrent</apiname></xref>. |
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20 The function updates the output parameter with the new file pointer position |
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21 in 64-bits. </p><p>Different modes of operation can be specified. These modes |
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22 are defined by <xref href="GUID-CA98DC2A-4B7D-336D-A251-C29120DDD444.dita"><apiname>TSeek</apiname></xref>.</p> </context> |
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23 <steps id="GUID-DFFBEA03-D0B8-55BB-97F4-6C2B68AB0276"> |
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24 <step id="GUID-AEA38679-553B-54C1-8DC7-1AAC09777C9A"><cmd>Use <codeph>TInt64</codeph> instead |
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25 of <codeph>TInt</codeph> for the offset from the location specified in <codeph>aMode</codeph>. </cmd> |
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26 <stepxmp><codeblock id="GUID-F64A228F-0D34-5EBA-9579-17C87BD8FCF0" xml:space="preserve">// Remove TInt filePosition = 0; |
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27 TInt64 filePosition = 0;</codeblock> </stepxmp> |
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28 </step> |
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29 <step id="GUID-A867C9DB-6DCE-53CF-9808-1866A64657C7"><cmd>To retrieve the |
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30 current position of the file pointer in a large file use <codeph>RFile::Seek64()</codeph> with |
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31 the mode <xref href="GUID-054ECFC9-C8C2-32B6-81DE-0526B3B17FF1.dita"><apiname>ESeekCurrent</apiname></xref>. </cmd> |
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32 <stepxmp><codeblock id="GUID-FFEA160C-2DB6-527B-89C7-ECD5D447974B" xml:space="preserve">TInt64 filePosition = 0; |
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33 // Remove r = file.Seek(ESeekCurrent, filePosition); |
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34 r = file.Seek64(ESeekCurrent, filePosition);</codeblock> </stepxmp> |
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35 </step> |
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36 <step id="GUID-F5738D61-A81A-542B-AC29-B9AE76785CEE"><cmd>To set the file |
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37 pointer to a particular positionwithin a large file use <codeph>RFile::Seek64()</codeph> with |
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38 the seek mode <xref href="GUID-458B652E-537A-3FC0-9DF7-396907A13522.dita"><apiname>ESeekStart</apiname></xref> and a seek position value that |
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39 is of type <xref href="GUID-AAE85115-A8AA-3F6C-BA8C-69F5A23B0D90.dita"><apiname>TInt64</apiname></xref>. </cmd> |
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40 <stepxmp><codeblock id="GUID-FFB160EE-6FE6-56C3-A486-0329BC9EFEC3" xml:space="preserve">TInt64 seekPos = 3000000000; |
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41 // Remove r = file.Seek(ESeekStart, seekPos); |
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42 r = file.Seek64(ESeekStart, seekPos);</codeblock> </stepxmp> |
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43 </step> |
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44 </steps> |
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45 <example><title>Seek position example</title> <p>If large file seek is required |
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46 use <xref href="GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7.dita#GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7/GUID-58F3EDD5-7DEF-38AA-A9B6-B68782B3FE83"><apiname>RFile64::Seek()</apiname></xref> instead of <xref href="GUID-BE0804F6-4375-3C8A-8C83-968F510466E0.dita#GUID-BE0804F6-4375-3C8A-8C83-968F510466E0/GUID-07136402-8D95-3256-9591-EE4141748E15"><apiname>RFile::Seek()</apiname></xref> and |
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47 use a TInt64 value to specify the location. </p> <codeblock id="GUID-24BE4FD9-A4C0-5AC9-9253-B810D7237189" xml:space="preserve"> // RFile file; |
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48 RFile64 file; |
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49 TInt err = file.Open(TheFs, _L(“BIGFILE.BIG”), EFileWrite); |
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50 if(err != KErrNone) |
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51 { |
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52 // We will only get here if a real error condition occurs. |
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53 return err; |
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54 } |
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55 |
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56 // Large file access is now supported! |
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57 // TInt seekPos = 0; |
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58 Tint64 seekPos = 0; |
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59 |
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60 // Seek the current position. This can be greater than 2GB. |
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61 err = file.Seek(ESeekEnd, seekPos); |
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62 if(err != KErrNone) |
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63 { |
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64 return err; |
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65 }</codeblock> </example> |
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66 </taskbody></task> |