How do I extract a single byte from within a string on iPhone?

In Android, I can extract a single byte from within a string using code like the following:

byte[] arrByte = String.get开发者_JAVA百科Bytes(); . 

If I wanted to do this on the iPhone in Objective-C, how could I accomplish the same task? Additionally, how could I get a byte for a given index in the string?

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If you take a look at the NSString reference you will get various methods to get the data from a string. An example is

NSData *bytes = [yourString dataUsingEncoding:NSUTF8StringEncoding];

You can also make use of the method UTF8String