====== Very brief guide to working with C ======


The following section has been tested on:
  - macOS High Sierra (10.13.6), Matlab 2014b, XCode 10.1
  - macOS Sierra (10.12.6), Matlab 2016b, Xcode 9.2 

One might have to work with C to meddle with low-level codes for softwares, or for developing new programs. There are different kinds of files for C:
  - source files (.c): The main code goes here. References some headers and object files. The source file is compiled to give us our program.
  - header files (.h): Function declarations, preprocessor statements.
  - object files (.o): Output of the compiler, but not executable by themselves, but its functions can be called by other programs without having to recompile the functions.
  - binary executable (.exe, .mex, etc..): executable output program. Mex (matlab executable) format is used by c source codes compiled for use by Matlab functions.

Refs: http://courses.cms.caltech.edu/cs11/material/c/mike/misc/compiling_c.html

===== Compiling in C  =====
To compile a source code into object or executive files, one uses a compiler (for instance, gcc or clang).
Flags:
  * [-c foo.c] : compiles the foo.c source file
  * [-o foo.o] : specifies the output of the compilation
  * [-g] : allows debuggers to be run on the output files
  * [-frameworks framework] : adds the framework libraries to be compiled with the source code.

===== Debugging in C (lldb or gdb) =====
In order to debug files in C on MacOS use lldb. On other systems, you can use gdb (gdb deosn't work as well on macOS).

Basic commands:
  * To import frameworks into the debugger (for instance, CoreGraphics for CG functions): <code> expr -l objective-c -- @import CoreGraphics </code>
  * step
  * p : evaluates an expression (same as expr)
  * parray : prints c arrays in a readable format

===== Debugging in C (Matlab mex files) =====
You can debug mex files that are called by matlab functions. 
The steps are outlined [[https://www.mathworks.com/matlabcentral/answers/299329-how-to-debug-mex-file-on-mac-platforms|here]] but I outline them here again. The debugging process works through XCode debugger, which can be programmed to be triggered by Matlab Executable. 

  - We want to debug a function whose source code is, for instance, mglPrivateSetGammaTable.c 
  - Recompile source mex file with debugging symbols (-g flag)<code> mex -g mglPrivateSetGammaTable.c </code>
  - Configure a new Xcode workspace for debugging
    - Create a new XCode workspace
      - Xcode > File > New > Workspace > Save with a name (e.g. mgl_debug) in an appropriate location (e.g. /User/josh/proj/mgl/mgllib). You can press Command+shift+G to find the folder 
    - Add the file(s) to be debugged
      - Drag and drop the file mglPrivateSetGammaTable.c to workspace
      - Uncheck "Destination: copy items into destination group's folder (if needed)"
    - Create a scheme
      - Product > Scheme > New Scheme
      - target: none > Name: debug> OK
      - Run > Info > Executable option "other" > Command + Shift + G > path to Matlab executable (e.g. /Applications/MATLAB_R2016b.app/Contents/MacOS/MATLAB_maci64)
      - Select "Wait for executable to be launched"
      - Close
    - Set a symbolic breakpoint (this allows the debugger not to stop on communication signals between the apps)
      - Debug > Breakpoints > Create Symbolic Breakpoint
      - Symbol: NSApplicationMain
      - Add action > type in: <code> process handle -p true -n false -s false SIGSEGV SIGBUS </code>
      - Check Automatically continue after evaluating
      - (If the editor disappears, right click on new breakpoint > edit breakpoint)
    - Set breakpoints in the mex file
      - View > Navigators > show project navigator > .c file to debug > click gutter to set breakpoints
  - Start the Xcode debugger
    - Product > Run
    - This should set the Xcode message on top of the Xcode window to "Waiting for MATLAB to launch"
  - Launch a new instance of matlab from terminal
    - Start Matlab executable from terminal (go to the path for the Matlab you indicated on the scheme) then type ./matlab
    - This should set the Xcode message on top of the Xcode window to "Running MATLAB: debug"
  - Run the mex file from Matlab in the terminal you just opened