How to detect whether a file is modified in iOS?

Question

How to detect whether a file is modified in iOS?

I don't mean the real-time monitoring, because while the application is gone, it won't detect anymore.

I've checked the attributes of the file, and couldn't find the satisfied one.(Did I miss something?)

There maybe some check-sum generating solutions, but they will require much time. (Is there any cheap check-sum generating algorithm?)

score 2 · Answer 1 · edited May 23 '17 at 12:12

2

You can use stat (reference), to get the modification time of the file. You could then compare it against your stored value:

struct stat sb;
if (stat("/path/to/file", &sb) == 0)
{
    ... compare sb.st_mtimespec with stored value

}
else
{
    ... report error
}

This question is pretty close to yours.

edited May 23 '17 at 12:12

Community

answered Feb 29 '12 at 07:38

trojanfoe

score 1 · Accepted Answer · answered Feb 29 '12 at 07:38

1

Which attributes did you check? With fstat(), you should be able to compare the st_mtime attribute of a file with a previously stored value.

answered Feb 29 '12 at 07:38

Alex Reynolds

Is it the same as the NSFileModificationDate? – Yun Feb 29 '12 at 07:55
It could be the same, but apparently `stat` works much faster. See the following SO answer that demonstrates the use of `stat` to get the modification date: http://stackoverflow.com/a/1999553/19410 – Alex Reynolds Feb 29 '12 at 08:06
It's not made clear, but that sample code looks like an Objective C category that extends `NSDate` (if you're interested in that detail). – Alex Reynolds Feb 29 '12 at 08:08
Ah, now I know why that was bothering me. I think if you try to send an app to Apple for approval, which contains a category that extends a class in an Apple API (like `NSDate`), then said app will be rejected. So I would use that code to learn `stat`, and then modify it into a method in a "local", non-Apple helper class. – Alex Reynolds Feb 29 '12 at 08:31

2 Answers2