Logging Information

Now that you’ve read the basics about classes and objects, it’s important to understand how to log information about them. In addition to printf, Objective-C offers a fundamental logging function called NSLog. This function works like printf and uses a similar format string, but it outputs to stderr instead of stdout. NSLog uses an NSString format string rather than a C string one.

NSStrings are declared differently than C strings. They are prepended with the @ (at) symbol. A typical NSString looks @"like this"; the equivalent C string looks "like this", omitting the @. Whereas C strings refer to a pointer to a string of bytes, NSStrings are objects. You can manipulate a C string by changing the values stored in each byte. NSStrings are immutable; you cannot access the bytes to edit them, and the actual string data is not stored within the object.