Comparing two xml files in Objective-C

Question

Hi there!

I have two xml files (a.xml and b.xml) in my file system (iPhone). Now I want to know if these files contain exactly the same data. Most of the time, this comparison would be true, because b.xml is the result of a copyItemAtPath: operation. Unless it is overwritten by newer information. What would be the most efficient way to compare these files?

1. I could read the contents of the files as strings and then compare the strings
2. I could parse the files and compare some key elements
3. I guess there is a very blunt way, that doesn't need to interpret the file, but allows me to compare on a lower level.

Any suggestion is very welcome.

Thanks ahead

Sjakelien

Update:

I ended up doing this:

oldData = [NSData dataWithContentsOfFile:PathToAXML];
newData = [NSData dataWithContentsOfFile:PathToBXML];

and then compare it with:

[newData isEqualToData:oldData];

The question is still: is that more efficient than:

oldData = [NSString dataWithContentsOfFile:PathToAXML];
newData = [NSString dataWithContentsOfFile:PathToBXML];

[newData isEqualToString:oldData];

Answer 1

One alternative to comparing the file contents is to track the file modification date -- if it's later than the date you created the copy, you might assume that it has been updated.

See fileAttributesAtPath:traverseLink: in the NSFileManager class.

Answer 2

This is a good start to getting a solution that matches your requirements: Coccoa xml parsing

Answer 3

BOOL filesAreEqual = [[NSData dataWithContentsOfMappedFile:file1] isEqual:[NSData dataWithContentsOfMappedFile:file2]];

Answer 4

Is there a reason you don't want to do something like an MD5 hash of the two files and compare the results - here is an example of some code that seems pretty common

http://stackoverflow.com/questions/840386/gravatar-for-iphone-how-do-i-generate-a-hexadecimal-md5-hash