Descriptor Length from File

[joseph.m]

Hi everyone,



I just want to know how can i avoid errors because of length overflow.


below is my code.

_LIT( KFileName, "c:\\Data\\Myfile.txt" );
TBuf<500> aText;
TBuf<200> filename;
filename.Copy(KFileName);
RFs fsSession;
User::LeaveIfError(fsSession.Connect());
RFile file;
if(BaflUtils::FileExists(fsSession, KFileName))
	{//open the existing
	if ( file.Open(fsSession, KFileName, EFileRead ) != KErrNone )
	          return;
	}
	else
	{//create new one
	file.Create(fsSession, KFileName, EFileWrite );
	}
CleanupClosePushL( file );                
RFileReadStream inputFileStream( file );
CleanupClosePushL( inputFileStream );
inputFileStream >> aText;
inputFileStream.Close();
file.Close();
CleanupStack::PopAndDestroy(2);
fsSession.Close();

the content of the file may exceed 500 chars how can i make the length dynamically conforms with the length of the chars written in the file?



Thanks,

Joseph

[symbianyucca]

the RFile does have Size() function that tells its size, then just use HBufC8 type buffer to read it into.

[joseph.m]

How can i?


If im right, declaring TBuf<N>, N should always a constant right?

can you give me an example code? pls

[symbianyucca]

HBufC8 is heap buffer, so check the SDK docs for it, it is constructed on run time, and you can give any lenght to it (up to avaialbe RAM amount of course)

[joseph.m]

Yup I know HBuf but in the line


inputFileStream >> aText;


aText should be declared as TBuf right?


HBuf variable can copy data

HBufC8* aUsr = HBufC8::NewL(aUser.Length());
CleanupStack::PushL(aUsr);
aUsr->Des().Copy(aUser);

is HBuf capable of copying by this syntax?


inputFileStream >> aUsr;


is this right?

[victor.xie]

Refer this example.
RFile file; // assume it is already open.
TInt size( 0 );
User:::LeaveIfError( file.Size( size ) );
if ( size != 0 )
{
HBufC8* buf = HBufC8::NewLC( size );
TPtr8 bufPtr( buf->Des() );
file.Read( 0, bufPtr ); // Or
inputFileStream >> bufPtr;
CleanupStack::PopAndDestroy();
}
Hope it can help you.

[joseph.m]

I can't exit the app without an error. It always returns an alloc error.


Here is my code

HBufC8* FilBuff(NULL);
		
TEntry MyEntry;
		User::LeaveIfError(fsSession.Entry(KHelloFileOut,MyEntry));
		
if(MyEntry.iSize > 0)
	{
	FilBuff = HBufC8::NewL(MyEntry.iSize);
	TPtr8 ReadPoint(FilBuff->Des());
fsSession.ReadFileSection(KHelloFileOut,0,ReadPoint,MyEntry.iSize);
	}

[symbianyucca]

you also need to remember to delete any heap-objects after you have done using them.

The Alloc error is just informing you that your app has memory leak in it.

[ykasidit]

Exactly,

If between the NewL and the delete doesn't have any leaving function, this would do:

FilBuff = HBufC8::NewL(MyEntry.iSize);
TPtr8 ReadPoint(FilBuff->Des());
fsSession.ReadFileSection(KHelloFileOut,0,ReadPoint,MyEntry.iSize);
delete FilBuff;

else, it's best to keep the habit of using the CleanupStack:

FilBuff = HBufC8::NewLC(MyEntry.iSize);
TPtr8 ReadPoint(FilBuff->Des());
fsSession.ReadFileSection(KHelloFileOut,0,ReadPoint,MyEntry.iSize);
CleanupStack::PopAndDestroy();//destroy the FillBuff that was pushed by NewLC

[AshramArzephucque]

You are aware that if you open a stream over your file and stream it into the HBufC then it will not work unless the contents of the file were created also by streaming into the file?

i.e. if it is a .txt file created by some other code/program/pc etc. then you cannot use streaming to read the contents. You will have to do a regular read from RFile.
Seems you're not streaming now, but originally were, so bear that in mind in case you switch back again.

[AshramArzephucque]

I disagree - it is not best to get into the habit of using the cleanup stack 'just in case'.
If everybody did that in all the code on the OS you would probably have thousands of unnecessary pushing/poppings adding processing overhead.

Exactly,

If between the NewL and the delete doesn't have any leaving function, this would do:

FilBuff = HBufC8::NewL(MyEntry.iSize);
TPtr8 ReadPoint(FilBuff->Des());
fsSession.ReadFileSection(KHelloFileOut,0,ReadPoint,MyEntry.iSize);
delete FilBuff;

else, it's best to keep the habit of using the CleanupStack:

FilBuff = HBufC8::NewLC(MyEntry.iSize);
TPtr8 ReadPoint(FilBuff->Des());
fsSession.ReadFileSection(KHelloFileOut,0,ReadPoint,MyEntry.iSize);
CleanupStack::PopAndDestroy();//destroy the FillBuff that was pushed by NewLC

[ykasidit]

Dear AshramArzephucque,

Thanks for pointing this out. I agree with you.

I apologize for my wrong statement, I see now that it's not "best" at all.

Best Regards.