I’m not sure if XCode 4 makes this technique unnecessary. Since I originally wrote this, I’ve seen XCode 4.0.2 stop at NSAssert on its own, without me setting this breakpoint. But it may be helpful to someone somehow. So here it is:

Xcode 3: Run Menu -> “Manage Breakpoints”
XCode 4: Go to the breakpoint navigator.

Click the + button at the bottom of the navigator, select “Add Symbolic Breakpoint…” from the contextual menu that appears.

In the “Symbol” box, enter

Then click “Done”. (NOTE: this is the default assertion handler. If you are using a custom assertion handler, you probably need to specify a symbol for its object and method.)

Now execution will break immediately on assertion failure. And very usefully, XCode shows the nearest source code of the stack, not the assembly of the assertion handler.

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