Getting Started with Code Analysis and Debugging - Xcode 4 - page 400

Creating custom messages
You can write a message to the console by including a call to printf anywhere in your code. For example,
printf(“This is a message”);
writes This is a message to the console. All of the standard printf formatting features are supported.
If you are writing Objective-C rather than C or C++, the NSLog function is more comprehensive. It includes
additional formatting and output options that aren't available in printf, at the cost of slightly clumsier syn-
tax. For example, to write a text string, you must prefix it with Objective-C's @ “objectification” feature:
NSLog(@”This is a message”);
NSLog supports the standard printf formatting features and adds a new one—the %@ option, which displays
information about an object. Table 15.1 summarizes the most useful options.
For example, to display the value of an integer use:
NSLog(@”Int value is: %i”, someInt);
To dump information about an object, use:
NSLog(@”%@”, someObject);
Note that the first @ prefixes the format and output string; the second @ selects the format.
This object logging feature has special properties. It runs a method called description on the object being
logged. Different objects implement description in different ways. For example, data collection objects
such as NSArray and NSDictionary dump their contents as text. For other objects, description de-
faults to the object's class name and memory address.
NOTE