Re: Opening a file read-only?
Re: Opening a file read-only?
- Subject: Re: Opening a file read-only?
- From: Wade Tregaskis <email@hidden>
- Date: Wed, 10 Aug 2011 08:10:52 -0700
> Try running fs_usage while your app is running, and you’ll be able to see what files it opens and in which modes.
> (Or there’s probably an Instrument for that now?)
There's half a dozen related to file I/O, which unfortunately makes it very awkward to use for even simple tasks like this. You also need to manually add in the VM instrument, since it's not in the "File Activity" template, in order to see the actual mmap. fs_usage is much faster.
On 10.7 -[NSData initWithContentsOfMappedFile:] opens the file read-only. So does -[NSData initWithContentsOfFile:]. Even if you instantiate an NSMutableData instead, the file is still opened read-only. I have not tested on iOS, but I'd be surprised if it were any different.
Note also that initWithContentsOfMappedFile: is deprecated in 10.7. There doesn't appear to be a replacement; I presume you're supposed to use initWithContentsOfFile:, but that really does read the entire file in at init time (into a single malloc allocation, no less)._______________________________________________
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