[R] Adding comment in C++ code for debugging purpose

[Christofer Bogaso]

Hi Ivan,

This is a very nice point. I will check this out.

Thanks and regards,

On Sat, Dec 17, 2022 at 1:53 PM Ivan Krylov <krylov.r00t using gmail.com> wrote:
>
> On Sat, 17 Dec 2022 05:02:33 +0530
> Christofer Bogaso <bogaso.christofer using gmail.com> wrote:
>
> > I am using an R package where there are some C++ code.
> >
> > To check some intermediate values generated by that C++ code, I added
> > a line like
> >
> > std::cout << "My values";
>
> A more efficient way of debugging C++ code running under R could be
> with the use of a C++ debugger. For example,
>
> 0) Make sure you have GDB (or a different debugger, e.g. lldb on a Mac)
> installed. You probably do, since you already have a working C++
> toolchain.
>
> 1) Run R using the command line: R -g gdb. The debugger will start and
> wait for your commands. Type: run. This will start R.
>
> 2) Type library(YOUR_PACKAGE_NAME) to load the package. You don't have
> to do it in this order (GDB can remember to set a breakpoint on a
> function that's not yet loaded in the address space), but this way you
> can be sure about the name of the function.
>
> 3) Press Ctrl-C, sending an interrupt to the application. GDB handles
> the interrupt and presents you with its prompt again. Type:
> break YOUR_FUNCTION_NAME. If the function name is right, GDB will tell
> you that a breakpoint is set. If not, it will ask you whether to
> postpone setting a breakpoint until the function shows up. Since the
> shared library should have been loaded by this time, the correct answer
> would be probably "no".
>
> 4) Type: continue. The debugger will give the control back to R. You
> can press Enter once and see R print the prompt symbol (">") again. Run
> your code that uses the package.
>
> 5) Eventually, you'll hit the breakpoint and find yourself in the
> debugger again. Like in the R browser, you can use "n" to step line by
> line, "s" to step inside function calls, and "c" to continue execution
> uninterrupted. You can also use "bt" and "frame NUMBER" to inspect the
> call stack and "print EXPRESSION" to see the values of various objects.
>
> A longer guide to GDB can be found at <https://beej.us/guide/bggdb/>.
> Telling GDB where the package source code is [*] will ease the process
> even further, as would obtaining debugging symbols and the source code
> for R itself.
>
> --
> Best regards,
> Ivan
>
> [*]
> https://sourceware.org/gdb/onlinedocs/gdb/Source-Path.html
> https://alex.dzyoba.com/blog/gdb-source-path/