On Thu, Oct 20, 2011 at 8:48 PM, Jens Alfke <j...@mooseyard.com> wrote:
> What’s unsafe is accessing file-mapped memory after the file becomes > unavailable. > If you use fread (or read), you’re not doing that. You're allocating your > own memory from the heap first, then copying data from the file into it. > There’s nothing dangerous about that. The memory will be available until you > explicitly free it. All the "f" Standard I/O calls return result codes. The calls will fail if your I/O fails for some reason, for example a disk being ejected after you've opened it but before you've had a chance to read it, or if you attempt to open a file only to find it missing. While Mac OS X discourages the user from dismounting filesystems that have open files on them, the user can forcibly dismount them. If nothing else, they can pull out a USB key, or disconnect a FireWire cable or ethernet cable over which one is getting data from a file server. Use "man fopen", "man fread", "man fwrite", "man fseek" and "man fclose" to see what the error codes are. To be robust in the face of I/O error, you will need to design your application well. This is not a trivial task for a novice. It takes some experience to learn how to do it. For C++, you would need to throw an exception on I/O error, then write exception-safe code. I have not yet really figured out the right way to do the equivalent for Objective-C, because Objective-C exceptions don't work like C++ exceptions do. You can pass result codes back to calling functions, but you have to be quite diligent about always doing so, always checking for results from the functions you call, then doing something sensible no matter what results your functions or methods or member functions return. -- Don Quixote de la Mancha Dulcinea Technologies Corporation Software of Elegance and Beauty http://www.dulcineatech.com quix...@dulcineatech.com _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
