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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 concept |
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11 PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
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12 <concept xml:lang="en" id="GUID-D71D0091-5C4E-5B2F-B1B6-783F11AB5021"><title>Writing to Large Files </title><shortdesc>This tutorial shows how to write to large files. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody><section><title>Introduction</title> <p>Files can be written to their current position or from a specified position, as discussed here: </p> <ul><li id="GUID-C5F51AAB-BC73-5B63-BE8B-F7142376C834"><p> <xref href="GUID-E9C763D4-AFFF-5D98-B82A-AF390A1B56A2.dita#GUID-E9C763D4-AFFF-5D98-B82A-AF390A1B56A2/GUID-559A2122-D5EF-53D3-9FA7-44F11B25D739"> Write() with relative/current position</xref> </p> </li> <li id="GUID-6C463908-6614-5D6E-94D5-52721E3F5759"><p> <xref href="GUID-E9C763D4-AFFF-5D98-B82A-AF390A1B56A2.dita#GUID-E9C763D4-AFFF-5D98-B82A-AF390A1B56A2/GUID-52200A55-E323-5C7D-99A2-86F61E4D7F32"> Write() with absolute position</xref>. </p> </li> </ul> </section> <section><title>Write() with relative/current position</title> <p>There are four <xref href="GUID-BE0804F6-4375-3C8A-8C83-968F510466E0.dita#GUID-BE0804F6-4375-3C8A-8C83-968F510466E0/GUID-7CA5896D-6FC2-32F4-96F8-864BDAC9861C"><apiname>RFile::Write</apiname></xref> overload functions relative/current position that allow you to specify a position greater than 2GB–1 by using the <xref href="GUID-AAE85115-A8AA-3F6C-BA8C-69F5A23B0D90.dita"><apiname>TInt64</apiname></xref> parameter. </p> <ul><li id="GUID-D5A71E59-F7FA-51D3-A85E-35D4E46D1A9F"><p> <xref href="GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7.dita#GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7/GUID-C7A290AB-3EA5-3F0E-A587-31E199F17855"><apiname>RFile64::Write(const TDesC8& aDes)</apiname></xref> </p> </li> <li id="GUID-9A023D6F-98B5-58D9-B0E2-38EAF3FC7AA6"><p> <xref href="GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7.dita#GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7/GUID-A9785313-9473-3CEE-A491-CFFDC3670F4D"><apiname>RFile64::Write(const TDesC8& aDes, |
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13 TRequestStatus& aStatus)</apiname></xref> </p> </li> <li id="GUID-8FFE6422-3957-57C8-BEAE-450D28FC70F6"><p> <xref href="GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7.dita#GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7/GUID-B8A1627D-48AB-38E4-9CFF-09447E20C6DA"><apiname>RFile64::Write(const TDesC8& aDes, TInt |
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14 aLength)</apiname></xref> </p> </li> <li id="GUID-0F0AFF90-0635-51C9-9B35-83E87E1A3F0C"><p> <xref href="GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7.dita#GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7/GUID-B0892D23-126A-3A84-B1D3-559572120491"><apiname>RFile64::Write(const TDesC8& aDes, TInt aLength, |
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15 TRequestStatus& aStatus)</apiname></xref>. </p> </li> </ul> <ol id="GUID-C64C5E8A-A481-5050-A415-ACE8CA0694D0"><li id="GUID-B61FB842-0C8D-5CB2-9BAC-FE033C216430"><p>Use <xref href="GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7.dita"><apiname>RFile64</apiname></xref> instead of <xref href="GUID-BE0804F6-4375-3C8A-8C83-968F510466E0.dita"><apiname>RFile</apiname></xref>. </p> <p><codeblock id="GUID-6A0E7FAD-2602-50DB-A200-3A3FB2CE7C56" xml:space="preserve">// RFile file; |
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16 RFile64 file;</codeblock> </p> </li> <li id="GUID-7CC3BEFE-19F7-5FB1-BB99-152A4911BA69"><p>Use <xref href="GUID-AAE85115-A8AA-3F6C-BA8C-69F5A23B0D90.dita"><apiname>TInt64</apiname></xref> variables in place of <xref href="GUID-7A2A43EC-6125-3BFE-834B-23C37F7B40D5.dita"><apiname>TInt</apiname></xref> variables where they may represent the number of bytes written. </p> <p><codeblock id="GUID-34FC7C71-EA56-5779-8E62-0729998AF405" xml:space="preserve">// Tint bytesWritten = 0; |
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17 Tint64 bytesWritten = 0;</codeblock> </p> </li> </ol> <p><b>Write with relative/current position example</b> </p> <p>The example below shows an application writing to locations greater than 2GB–1. The <xref href="GUID-BE0804F6-4375-3C8A-8C83-968F510466E0.dita"><apiname>RFile</apiname></xref> class has been replaced with <xref href="GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7.dita"><apiname>RFile64</apiname></xref> and the <xref href="GUID-7A2A43EC-6125-3BFE-834B-23C37F7B40D5.dita"><apiname>TInt</apiname></xref> variable that represents the number of bytes written has been changed to <xref href="GUID-AAE85115-A8AA-3F6C-BA8C-69F5A23B0D90.dita"><apiname>TInt64</apiname></xref>. </p> <codeblock id="GUID-2EA7CE6A-C264-54A4-98C8-9AD9C57CBB05" xml:space="preserve"> // RFile file; |
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18 RFile64 file; |
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19 TInt err = file.Open(TheFs, _L(“BIGFILE.BIG”), EFileWrite); |
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20 if(err != KErrNone) |
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21 { |
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22 // We will only get here if a real error condition occurs. |
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23 return err; |
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24 } |
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25 |
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26 // Tint bytesWritten = 0; |
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27 Tint64 bytesWritten = 0; |
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28 TBuf8<1024> writeBuf; |
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29 ... |
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30 |
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31 FOREVER |
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32 { |
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33 // Fill buffer with input data |
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34 r = prepareBuffer(writeBuf); |
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35 if(KErrNone != r) |
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36 { |
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37 // No data to write! |
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38 break; |
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39 } |
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40 |
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41 r = file.Write(writeBuf); |
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42 if(r != KErrNone) |
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43 { |
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44 // Error handling |
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45 } |
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46 bytesWritten += writeBuf.Length(); |
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47 }</codeblock> </section> <section><title>Write() with absolute position</title> <p>There are four <xref href="GUID-BE0804F6-4375-3C8A-8C83-968F510466E0.dita#GUID-BE0804F6-4375-3C8A-8C83-968F510466E0/GUID-7CA5896D-6FC2-32F4-96F8-864BDAC9861C"><apiname>RFile::Write</apiname></xref> overload functions with absolute position that allow you to specify a position greater than 2GB–1 by using the <xref href="GUID-AAE85115-A8AA-3F6C-BA8C-69F5A23B0D90.dita"><apiname>TInt64</apiname></xref> parameter. </p> <ul><li id="GUID-D9692C56-D4D1-5068-AE4F-0D8209ABE2B5"><p> <xref href="GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7.dita#GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7/GUID-F2DDC64C-2BB3-3944-8377-F2FCAFF2C36B"><apiname>RFile64::Write(TInt64 aPos, const TDesC8& |
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48 aDes)</apiname></xref> </p> </li> <li id="GUID-1C749FBD-5403-59A1-8443-5144B94DBC29"><p> <xref href="GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7.dita#GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7/GUID-52602FFB-4319-3148-A559-C660C59D5409"><apiname>RFile64::Write(TInt64 aPos, const TDesC8& aDes, |
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49 TRequestStatus& aStatus)</apiname></xref> </p> </li> <li id="GUID-8D20B3ED-DE4A-5C77-8453-CDC221CDCBD3"><p> <xref href="GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7.dita#GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7/GUID-9834C13E-50A4-3659-B301-C89C6F71C4CA"><apiname>RFile64::Write(TInt64 aPos, const TDesC8& aDes, TInt |
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50 aLength)</apiname></xref> </p> </li> <li id="GUID-90B8A6B7-15E0-5ADF-98DA-889D2994E9FB"><p> <xref href="GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7.dita#GUID-83A415A0-F417-3CA5-BA10-5AEF119AB1F7/GUID-9A3724AB-9B48-35F4-AE97-CB77AC2D1A1B"><apiname>RFile64::Write(TInt64 aPos, const TDesC8& aDes, TInt |
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51 aLength, TRequestStatus& aStatus)</apiname></xref>. </p> </li> </ul> <ol id="GUID-2A682DB4-5D52-5EE1-96CC-AFD56B577E5C"><li id="GUID-D0169894-B983-5C3A-A0E6-CA76BB48EA7F"><p>Use a <xref href="GUID-AAE85115-A8AA-3F6C-BA8C-69F5A23B0D90.dita"><apiname>TInt64</apiname></xref> instead of a <xref href="GUID-7A2A43EC-6125-3BFE-834B-23C37F7B40D5.dita"><apiname>TInt</apiname></xref> for the write position. </p> <p><codeblock id="GUID-EE36228D-DDFD-52AD-8BA4-0C8AF38C7DD2" xml:space="preserve">// TInt writePosition = 0; |
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52 TInt64 writePosition = 0;</codeblock> </p> </li> <li id="GUID-709912EA-32E0-5E7B-A187-7C39AEB13373"><p>Replace RFile with RFile64. </p> <p><codeblock id="GUID-EA9C17D0-64D1-571F-BEC2-71574B843148" xml:space="preserve">// RFile file; |
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53 RFile64 file;</codeblock> </p> </li> </ol> <p><b>Write with absolute position example</b> </p> <p>To write to locations beyond 2GB–1 the file must be opened for 64-bit access and <xref href="GUID-7A2A43EC-6125-3BFE-834B-23C37F7B40D5.dita"><apiname>TInt</apiname></xref> variables should be replaced with <xref href="GUID-AAE85115-A8AA-3F6C-BA8C-69F5A23B0D90.dita"><apiname>TInt64</apiname></xref>. </p> <codeblock id="GUID-27FAE59A-F150-54B9-AC95-BA588552E605" xml:space="preserve"> // RFile file; |
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54 RFile64 file; |
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55 TInt err = file.Open(TheFs, _L(“BIGFILE.BIG”), EFileWrite); |
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56 if(err != KErrNone) |
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57 { |
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58 // We will only get here for upon encountering a real error condition. |
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59 return err; |
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60 } |
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61 |
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62 // TInt writePosition = 0; |
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63 TInt64 writePosition = 0; // Use a TInt64 to prevent wrap-around |
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64 TBuf8<1024> writeBuf; |
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65 ... |
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66 FOREVER |
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67 { |
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68 // Fill buffer with input data |
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69 r = prepareBuffer(writeBuf); |
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70 if(KErrNone != r) |
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71 { |
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72 // No data to write! |
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73 break; |
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74 } |
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75 |
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76 r = file.Write(writePosition, writeBuf); |
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77 if(r != KErrNone) |
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78 { |
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79 // We will only get here upon encountering a real error condition. |
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80 return r; |
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81 } |
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82 writePosition += writeBuf.Length(); // Must use a TInt64 |
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83 }</codeblock> </section> </conbody></concept> |