About 2000 strings to a file - iphone

Question

I need to put separate lines into a file, but it seems that it's not supported by
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
// the path to write file
NSString *appFile = [documentsDirectory stringByAppendingPathComponent:#"myFile"];
[dataString writeToFile:appFile atomically:YES];
It does put a string to a file but it overwrites previous one.
Any suggestions?

Answer 1

To append data to an existing file, create an NSFileHandle instance for that file, then call -seekToEndOfFile and finally -writeData:. You'll have to convert your string into an NSData object yourself (with the correct encoding). And don't forget to close the file handle when you're finished.
The easier, but also less efficient way, is to read the existing file contents into a string, then append the new text to that string and write everything out to disk again. I wouldn't do that in a loop that executes 2000 times, though.

Answer 2

Thanks Ole! That's what I've been looking for.
Some sample code for the others:
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
//creating a path
NSString *appFile = [documentsDirectory stringByAppendingPathComponent:#"nameOfAFile"];
//clearing or creating (NSFileHande doesn't support creating a file it seems)
NSString *nothing = #""; //remember it's CLEARING! so get rid of it - if you want keep data
[nothing writeToFile:appFile atomically:YES encoding:NSUTF8StringEncoding error:nil];
//creating NSFileHandle and seeking for the end of file
NSFileHandle *fh = [NSFileHandle fileHandleForWritingAtPath:appFile];
[fh seekToEndOfFile];
//appending data do the end of file
NSString *dataString = #"All the stuff you want to add to the end of file";
NSData *data = [dataString dataUsingEncoding:NSASCIIStringEncoding];
[fh writeData:data];
//memory and leaks
[fh closeFile];
[fh release];
[dataString release];