Question

I have the following problem in objective C: In a larger context I would like to search in a String for a substring and get the position, where the first such substring is located. I also want the search to start from the back. so for example:
calling the desired function on “K123K” with searching “K” should result in 3, because I start from the back.

In My Code it’s more efficient to search through a NSData object, because that is what I read in. So I tried a little test code out to see if my proposed method works:

    NSString *testString = @"01K234567K";
    NSData *testData = [testString dataUsingEncoding:NSUTF8StringEncoding];
    NSString *testLetter = @"K";
    NSData *kData = [testLetter dataUsingEncoding:NSUTF8StringEncoding];
    NSRange whereisK = [testData rangeOfData:kData options:NSBackwardsSearch      range:NSMakeRange(0, [testData length])];
    NSLog(@"loc: %d, len: %d",whereisK.location,whereisK.length);

The result is against my expectations, it seems like rangeOfData starts searching still from the front:

    loc: 2, len: 1

I really don’t know what I am doing wrong. It seems like NSBackwardsSearch is not doing its job as an option! I happy for any help or suggestions…

Answer 1

The correct value for the option is NSDataSearchBackwards. The option you are using is used for NSString searches. You can read about it the NSData documentation.