On May 10, 2014, at 2:06 PM, William Squires <wsqui...@satx.rr.com> wrote:
> If I have an NSString that contains a filename (and possibly a path, as typed
> on the command-line), how can I check to see if the specified file actually
> exists?
[ code fragment that collects a string representing a file name (not an
absolute path) from argv[] ]
> How can I make sure MyFile.txt exists before trying to read it in?
1. See -[NSFileManager fileExistsAtPath:] or -fileExistsAtPath:isDirectory:.
Careful practice would be to convert the partial path to an absolute one. Xcode
handles working directories differently than the shell does.
2. Don’t do it. In the time between detecting the presence (or not) of the file
and the time you attempt (or don’t) to read it, the file may have been deleted
(or created). Preflighting file access works, until it doesn’t, when something
happens that is nearly impossible to reproduce, or malware takes advantage of
the gap.
Just attempt the read. If the file doesn’t exist then, you’ll be given an error
or exception that will tell you so. Errors and exceptions are there to help
you. It’s not much harder to write, and it works.
— F
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