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<concept xml:lang="en" id="GUID-00025EAD-C4B6-5408-96A3-FFDBBBDC7CAB"><title>How to read and write a file</title><prolog><metadata><keywords/></metadata></prolog><conbody><p>Reading transfers data from a file to a descriptor, and writing transfers data from a descriptor to a file. </p> <p>Use <xref href="GUID-BE0804F6-4375-3C8A-8C83-968F510466E0.dita#GUID-BE0804F6-4375-3C8A-8C83-968F510466E0/GUID-94CCC141-8E26-3FA3-A222-D9A658AEA8A9"><apiname>RFile::Read()</apiname></xref> to read, and <xref href="GUID-BE0804F6-4375-3C8A-8C83-968F510466E0.dita#GUID-BE0804F6-4375-3C8A-8C83-968F510466E0/GUID-325997F1-3252-358E-B278-44D3A5418FAC"><apiname>RFile::Write()</apiname></xref> to write. </p> <codeblock id="GUID-28737C7A-70BA-5AA8-A4DC-0075A59CCB59" xml:space="preserve">// Open file1

_LIT(KMyFile,"c:\\documents\\file1");

RFile myFile;

User::LeaveIfError(myFile.Open(fs,KMyFile,EFileShareExclusive|EFileWrite

));

// Write to current file position: start of file

_LIT8(KWriteBuf,"write data");

myFile.Write(KWriteBuf);

// Read from position 0: start of file

TBuf8<6> readBuf1;

myFile.Read(0,readBuf1); // readBuf1 is now "write "

// Read from current position

TBuf8<4> readBuf2;

myFile.Read(readBuf2);      // readBuf2 is now "data"

</codeblock> <section><title>Notes</title> <ul><li id="GUID-3F823A12-E192-5381-B8CC-FF377B1CEC0D"><p>In all cases, the file data is treated as binary and byte descriptors are used (TDes8, TDesC8). Thus, file operations are not dependent on the Unicode/non-Unicode build variant. </p> </li> <li id="GUID-0A6255A4-12EC-5F60-9071-E001EA137585"><p>There are several variants of both <codeph>Read()</codeph> and <codeph>Write()</codeph>. The basic <codeph>Read(TDes8&amp; aDes)</codeph> and <codeph>Write(const TDesC8&amp; aDes)</codeph> are supplemented by variants allowing the descriptor length to be overridden, or the seek position of the first byte to be specified, or asynchronous completion, or any combination. </p> </li> </ul> </section> </conbody></concept>