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Hands-On XCode Debugging

Having used the interactive python debugger ipdb for my Python projects, I missed having a REPL in the standard Objective-C IDE. Fortunately, XCode comes equipped with a REPL called LLDB.

After adding a breakpoint in your code, you can interact with your code using LLDB commands in the bottom right window as shown in the following screenshot:

LLDB is in the bottom right window

Here are a couple basic LLDB commands that I’ve found useful:

po (prints output)
n/next (step over)
s/step (step into)
c/continue (continues execution)
expr (for functions and expressions)

You can also define new breakpoints dynamically, add watchlists to monitor variables, and more. See the full command reference.

For a good look at how to use Xcode’s debugging features, all powered by the LLDB debugging engine, see the WWDC 2013 session video for Tools #407 WWDC 2013: Debugging with Xcode.

To see the latest advanced techniques to help you efficiently track down bugs with LLDB, view the WWDC 2013 session video for Tools #413 WWDC 2013: Advanced Debugging with LLDB.

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