[Rcpp-devel] R.e. Debugging Rcpp packages with GDB

[Dirk Eddelbuettel]

On 18 January 2011 at 15:52, Christian Gunning wrote:
| On Tue, Jan 18, 2011 at 2:46 PM,
| <rcpp-devel-request at lists.r-forge.r-project.org> wrote:
| >
| > Can people share any tricks they use to debug Rcpp packages? For example, can I "print" variables in a format that's a bit more high-level, like something that I would get if I sent them to "cout"?
| >
| 
| It's not very sophisticated, but I find that much of the time adding
| Rf_PrintValue(xx) calls to code gives me as much info as I need.  If
| it's a non-SEXP object like int, then Rf_PrintValue(wrap(my_int)).
| 
| > If that's not entirely obvious from my question, I am not a GDB expert. :-) Basically, my workflow is: "attach to the R process", "set a breakpoint at the function entry point", "single-step and print variable values". I have used watches and conditional breakpoints in GUI debuggers, but not (yet) in gdb. Are there any Rcpp-specific gotchas to using those features with GDB?
| 
| I have 2 related "simple questions" after reading through Chapters 1
| and 4 of "Writing R Extensions":
| 
| My build/test chain is:
| 
| R CMD INSTALL mypackage
| R --vanilla --debugger gdb
| run
| require(mypackage)
| <test in R>
| quit()
| <edit code>
| R CMD INSTALL mypackage
| run
| require(mypackage) ## reload package with edits
| <lather, rinse, repeat>
| 
| 1)  Is there a "best" way to reload the shared library after
| rebuilding it? dyn.unload() and dyn.load()?

I am partial to littler. Eg sometimes I just do

  $ R CMD INSTALL foo && r -lfoo -e'someExpressionIWantToTest()'
 
Because the 'r' (littler) starts fresh sessions I do not need to worry about
unload.   In other cases I use inline -- it depends.

| 2) Is there a simple way to include debugging symbols/keep values from
| getting optimized out when building with Rcpp?

You could always include -g and then strip what you don't need -- which is 
what Debian and Ubuntu do to give you the *-dbg packages.  

R sits on top of Makefile logic, and make is pretty powerful language.  You
can (literally) do just about anything....   Setting CFGLAGS / CXXFLAGS or
their PKG_* variants is probably easiest.

Dirk

-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com