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Re: [Newbie] Basic file handling questions...

Hi Martin,

There are a few things you might need to do first...

On Thursday, November 8, 2001, at 07:09 AM, Martin-Luc Girard wrote:
What I'm trying to do is read from a plain text file containing 50 characters per line, and this, one line at a time...

First of all, am I doing this correctly when opening my file?

NSString *filePath= @"~/database.txt";
NSMutableString *fileContents= [[NSMutableString alloc] initWithString: @""];
NSFileHandle *theFile;

theFile = [NSFileHandle fileHandleForReadingAtPath: filePath];

Close - What's happening here is that your program is looking in its current working directory for a directory called "~" and then within that a file called "database.txt" -
Since it's not finding it, you're getting back nil for theFile.

First, you'll have to expand the ~ out in the path:

NSString *expandedPath = [filePath stringByExpandingTildeInPath];

and then pass expandedPath along to [NSFileHandle fileHandleForReadingAtPath:].

Now the file's opened.

[fileContents initWithCString:[theFile readDataToEndOfFile]];

definitely does not work...

Well, you've already sent an init message (in this case initWithString:) once to fileContents. Here, you're sending another one (initWithCString) to it. You only want to init once. But... you only need the string if you've got the data - for the case where you want to get the whole file, you can say

NSData *rawFileContentsAsNSData = [fh readDataToEndOfFile];
NSString *fileContents
if( rawFileContentsAsNSData ) {
fileContents = [[NSString alloc] initWithData:rawFileContentsAsNSData encoding:[NSString defaultCStringEncoding]];
}

(I'm using NSString here, since once I've got the data into the string, I'm not going to be changing the string - I'll let NSFileHandle take care of creating the NSData for me that's the right size).

When I'm done with the fileContents string, I should send it a release message. I could also have said

fileContents = [[NSString alloc] initWithData:rawFileContentsAsNSData encoding:[NSString defaultCStringEncoding] autorelease];

Which will cause fileContents to be released at a later time.

How would I read a 50 character lines?

NSFileHandle allows you to read from the file using its readDataOfLength: method as well -

NSData *one50CharacterLine = [fh readDataOfLength:50];

This returns up to 50 -bytes- - so these comments apply to ASCII text. If your file is non-ASCII (Unicode, etc) then you'll have to adjust the length you read accordingly.

Finally, to close the file... is the following correct?

[theFile closeFile];

Yes, but it does not deallocate the NSFileHandle object - for that you need [theFile release]; afterward.

.chris

--
Chris Parker <email@hidden>
Cocoa Frameworks Engineer
Catapultum habeo. Nisi pecuniam omnem mihi dabis, ad caput tuum
saxum immane mittam.

References: 
 >[Newbie] Basic file handling questions... (From: Martin-Luc Girard <email@hidden>)



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