How To Interactively Debug C

I had a bit of an journey yesterday getting gdb, (an interactive debugger for gcc) compiling and working in Sublime Text 3 (via the SublimeGDB package), so I thought I should document the issues I ran into & what finally worked, for others and perhaps my future self.

When I first installed the SublimeGDB package and tried to run it, nothing seemed to happen, so I went to View -> Show Console and saw a the directory is invalid error. I googled a bit and ended up following the instructions here to get it to work: instead of setting the workingdir to ${folder:${file}} or ${folder:${project_path:your_executable_name}}, as the default settings seem to suggest -- or even ~/..., I ended up using an absolute path ("/Users/my-user-name/...) and specifying these other settings in my *.sublime-project file:

{
    "folders":
    [
        {
            "path": "."
        }
    ],
    "settings": {
        "sublimegdb_commandline": "gdb --interpreter=mi ./beast",
        "sublimegdb_workingdir": "/Users/prust/repos/beast.c",
        "sublimegdb_exec_cmd": "-exec-run",
        "tab_size": 8,
        "sublimegdb_i_know_how_to_use_gdb_thank_you_very_much": true
    }
}

Then I got an error about it not being able to find gdb (command not found, I think), which indicated the gdb wasn't installed on my system. I tried installing it via Homebrew (brew install gdb), which appeared to work, but when I tried to use it, it failed with this error:

dyld: Library not loaded: /usr/local/opt/mpfr/lib/libmpfr.6.dylib
  Referenced from: /usr/local/bin/gdb
  Reason: image not found

This *.dylib library wasn't on my machine; I'm guessing (and this is just speculation; I don't actually know how Homebrew works) that Homebrew installed a pre-compiled version of gdb which depended on a library that existed on the machine it was compiled with, but did not exist on my machine.

I was able to address this by compiling gdb myself -- first, I downloaded & tried to compile the latest version (8.1) from http://ftp.gnu.org/gnu/gdb/. There were 150 warnings and 1 error, which was buried in the warnings & I couldn't find by searching the console because the warnings had the word "error" in them too. Then I downloaded & compiled the previous version (7.12), via running ./configure and make and, in spite of a ton of warnings, it compiled! I installed it (I think via sudo make install) and then followed the instructions here to generate a CodeSigning certificate on macOS, to configure the OS to always trust the cert and to sign the newly-installed gdb executable with the cert.

So, after over an hour of wrestling, I was finally able to run the gdb debugger from Sublime. It ran to the breakpoint and then I was able to use the step and next commands to walk through the code. It took about 60 seconds to find & fix the bug in my game (a clone of the classic action/block-pushing game, Beast).