debugging C++ in XCode

I've been frustrated by how XCode's debugger seems to be easily confused by C++. Also generally annoyed that it's hard to view the contents of an array by unfolding arrows. Things are moving along much more nicely now that I've started paying more attention to the command-line interface to GDB, the debugging tool beneath xcode's debugger gui.

For example, when trying to inspect a variable, I was getting this error: "current stack frame does not contain a variable named `self'. The problem was that GDB thought it was looking at ojective-c when in fact it was C++. The fix was to manually tell GDB via the console that it's looking at C++.

set language c++

The GDB command line interface is also really nice for examining buffers. When working with audio, you get deal with huge sets of data, tens of thousands of samples. There's no obvious way to examine that data via the debugger ui. Even harder, what if you want to examine a small chunk of it somewhere in the middle. With the GDB console, I can type this:

(gdb) x/64f sample.data_ + sampleReadPosition

Where sample.data_ is my audio data and sampleReadPosition is where I want to start looking. A few more things about this command: x is the main command which inspects data. /64 means repeat 64 times, and format as a float. So this command says: look at the memory pointed to by sample.data, jump forward by sampleReadPosition step, and format it as a float.

Here's the output.

0xbd9b458: 0.0132450331 0.0792260543 0.0219122898 0.0856349394

0xbd9b468: 0.0309457686 0.0916776061 0.0396130271 0.0969878212

0xbd9b478: 0.0487075411 0.101870783 0.0573747978 0.106387526

0xbd9b488: 0.0656758323 0.110171817 0.0739768669 0.113162637

0xbd9b498: 0.0818506405 0.115421005 0.0890530124 0.116946928

0xbd9b4a8: 0.0958281234 0.117313154 0.102237009 0.117313154

0xbd9b4b8: 0.107913449 0.116214484 0.112796411 0.114322335

0xbd9b4c8: 0.116946928 0.111270487 0.119998783 0.107547231

0xbd9b4d8: 0.122623369 0.102969453 0.1241493 0.0977202654

0xbd9b4e8: 0.124515519 0.0916776061 0.1241493 0.0845362693

0xbd9b4f8: 0.122989595 0.076967679 0.120731227 0.0686666444

0xbd9b508: 0.117313154 0.0596331693 0.11358989 0.0505386516

0xbd9b518: 0.108279675 0.0404065065 0.102603227 0.0302133244

0xbd9b528: 0.0961943418 0.0200201422 0.0886867866 0.00909451582

0xbd9b538: 0.0807519779 -0.00146488845 0.0724509433 -0.0124515519

0xbd9b548: 0.0634174645 -0.0230109561 0.0539567247 -0.0335703604

The GDB manual is here.

If you find yourself working outside the cocoa frameworks (and perhaps even if you don't), I highly recommend digging in to GDB.