Question

I’m working with Xcode 4 and I’d like my iphone 4 application to append a line to a file every time I run a test. Is there any fast way to do this? If so, where exactly am I allowed to write inside the iphone directory hierarchy?

Thanks.

Answer 1

You can’t write inside the bundle of the iPhone application because that would break encryption. You can write in the Documents directory, or somewhere under <apphome>/Library.

Since Documents may become visible for the iTunes user if you add UIFileSharingEnabled to your Info.plist, and this is a file private to the application, adding the file under Library is better. Not that it matters much during testing. Apple documents related to this: Technical Q&A QA1699: Storing Private Data, A Few Important Application Directories.

You can use this code in an iPhone application to append text to a file:

// get path to Documents/somefile.txt
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *path = [documentsDirectory stringByAppendingPathComponent:@"somefile.txt"];

// create if needed
if (![[NSFileManager defaultManager] fileExistsAtPath:path]){
    [[NSData data] writeToFile:path atomically:YES];
} 

// append
NSFileHandle *handle = [NSFileHandle fileHandleForWritingAtPath:path];
[handle truncateFileAtOffset:[handle seekToEndOfFile]];
[handle writeData:[@"line of text\n" dataUsingEncoding:NSUTF8StringEncoding]];