Reading and writing files

Comments

Inefficient

This is a very inefficient way of writing/reading to/from files. You have to use asynchronous operations to do read/write files.

WriteToFileL

You have to use Seek() to position file cursor at the end of the file if you do not want to get the data at the begining overwritten.

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16 Sep
2009

Article Review by savaj (20090916)

Application may need to save some text data on client. Flat text file is more suitable in storing large data. Creating a text file and saving text data, in it for later use, is good option. Reading and writing text file is basic operation to use text file. RFile is key API to read/write data from/in file.

The article describes methods to read data from text file and write data to a text file. This article use synchronous method RFile::Read() and RFile::Write() to read/write data in file, However if content of text file is large then it is recommended to use asynchronous method RFile::Read() and RFile::Write().

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Article Metadata

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Article

Created: symbianyucca (22 Mar 2007)

Last edited: hamishwillee (12 Jan 2012)

RFile is the base API for file reading and writing, it is quite simple to use as following code sample shows:

Header required:

#include <f32file.h>

Library needed:

LIBRARY    efsrv.lib

Source:

HBufC8* ReadFromFileL(const TDesC& aFile)
{		
	HBufC8* FilBuff(NULL);
 
	RFile ReadFil;
 
        /*Open file for reading */
	if(KErrNone == ReadFil.Open(CCoeEnv::Static()->FsSession(),aFile,EFileRead))
	{	
		CleanupClosePushL(ReadFil);
 
		TInt FilSiz(0);
		if(ReadFil.Size(FilSiz) == KErrNone)
		{
			if(FilSiz > 0)
			{
				FilBuff = HBufC8::NewL(FilSiz);
				TPtr8 ReadPoint(FilBuff->Des());
 
				ReadFil.Read(ReadPoint,FilSiz);
			}
		}
 
		CleanupStack::PopAndDestroy(1);//ReadFile
	}
 
	return FilBuff;
}

With this function you can read the whole content of the file into a HBufC byte buffer. Note that the name has to be full name (drive+path+name+extension). One problem with this approach is that if the file is open it will not work, then instead you could use the RFs API directly as shown in this sample:

HBufC8* ReadOpenFileL(const TDesC& aFile)
{		
	HBufC8* FilBuff(NULL);
 
	TEntry MyEntry;
	User::LeaveIfError(CCoeEnv::Static()->FsSession().Entry(aFile,MyEntry));
 
	if(MyEntry.iSize > 0)
	{
		FilBuff = HBufC8::NewL(MyEntry.iSize);
		TPtr8 ReadPoint(FilBuff->Des());
 
		CCoeEnv::Static()->FsSession().ReadFileSection(aFile,0,ReadPoint,FilSiz);
	}
 
	return FilBuff;
}

The ReadFileSection reads the file without opening the file. And to write a file, you could use the RFile API by doing something like this:

void WriteToFileL(const TDesC& aFile,const TDesC8& aData)
{		
	RFile ReadFil;
 
	/* Open file if it exists, otherwise create it and write content in it */
	if(BaflUtils::FileExists(CCoeEnv::Static()->FsSession(),aFile))
		User::LeaveIfError(ReadFil.Open(CCoeEnv::Static()->FsSession(),aFile,EFileWrite));
	else
		User::LeaveIfError(ReadFil.Create(CCoeEnv::Static()->FsSession(),aFile,EFileWrite));
 
	CleanupClosePushL(ReadFil);
 
	TInt position = 0;
        /*Set cursor at the end of the file to write content at the end of file on each successive call to write() method. */
	User::LeaveIfError(ReadFil.Seek(ESeekEnd, position));
 
        /*To write content in next line on successive call to write() method. */
        User::LeaveIfError(ReadFil.Write(_L8("\r\n")));
 
        /*Write actual content to file. */
	User::LeaveIfError(ReadFil.Write(aData));
 
	CleanupStack::PopAndDestroy(1);//ReadFile
}

This implementation appends to the existing file or creates new file if file does not exist. In case you want to replace already existing file, then you can use RFs API’s Delete()-function to delete the file or Replace()-function from the RFile.