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iosobjective-ccocoa-touchnsrange

NSRangeException when searching for bytes near end of NSData

I want to check the last 2 bytes of files in my app to make sure they are not corrupt .jpg's

rangeOfData:options:range: looks like a good option, but I am having a hard time figuring out how to get a proper NSRange. The range I am looking for is starting near the end of the NSData, up to the end.

Here is what I have so far:

NSData *imageData = [NSData dataWithContentsOfFile:filePath];
NSRange range = {([imageData length]-8),[imageData length]};
NSString *str = @"FFD9";
NSData *jpgTest = [str dataUsingEncoding:NSUTF8StringEncoding];
NSRange found = [imageData rangeOfData:jpgTest options:NSDataSearchBackwards range:range];

Here is the error I get:

** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[NSConcreteData rangeOfData:options:range:]: range {14954, 14962} enxceeds data length 14962'

How do I properly get the range to search the last few bytes of my NSData?

Solution

  • The second member of NSRange is not the end point of the range but its length. So in your case it should be:

    NSRange range = {([imageData length]-8), 8};