Re: [R-pkg-devel] Error checking in an independent C code and printing (perror, printf, etc.)
On 05/09/2022 10:48 p.m., Jiří Moravec wrote: Hello, this is my first time writing C code that interacts with R. To make my C code more modular, reusable, and easier to test with unittests, I split my code into: a) code that does stuff b) code that interfaces between a) and R. Only the b) imports the R headers, a) is completely independent of R (and potentially shared between different projects). That brings me to a problem: How to do error handling in C without the use of various C-specific print functions R-specific print functions? The C-specific print functions raise a CRAN note: Compiled code should not call entry points which might terminate R nor write to stdout/stderr instead of to the console, nor use Fortran I/O nor system RNGs But R(C) print functions cannot be used without importing particular header, which would induce otherwise another dependency, and tie it closely with R. I think the best way is to think of error reporting as part of the interface. Your code that does stuff shouldn't try to print anything, it should just return special error code values to indicate problems. The code in b) looks for those error codes and creates R messages or errors. If you use the a) code in a different project, it would do the same, but report the errors in whatever way is natural in that context. This is my first time writing into mailing list, hopefully I am doing everything ok. Looks fine to me! Duncan Murdoch __ R-package-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-package-devel
Re: [R-pkg-devel] Error checking in an independent C code and printing (perror, printf, etc.)
Hello Jiří and welcome to the mailing list! On Tue, 6 Sep 2022 14:48:02 +1200 "Jiří Moravec" wrote: > That brings me to a problem: How to do error handling in C without > the use of various <...> R-specific print functions? (Assuming that's what you meant...) One way would be to introduce callbacks from the R-independent part to the R-interfacing part, but I can imagine this to require tedious boilerplate. Also, many of R's entry points can raise an error condition (e.g. if an allocation fails), which would result in a longjmp() away from your code. Any resource not known to R's garbage collector is going to be leaked in this situation. I think you're actually allowed to format strings using sprintf and friends; only actual printing to stdout/stderr is disallowed because the user may be using e.g. Rgui on Windows and not see it at all. If you need to print error messages, you can pass them to the R side as strings, probably in storage allocated by the caller to avoid leaks on errors. Error codes are of course an option too, but can be less informative if not accompanied by an explanation of what went wrong. (It's considered polite for package code to use R's message system not only because of the stdout/Rgui problem mentioned above, but also because it gives the user an option to run your code with suppressMessages() and disable the verbose output. When the R code directly calls cat() or the C code prints directly to console, that option disappears.) To summarise, R would accept any option where only R is interacting with the user (or doing other I/O). If neither of this is satisfying, can you provide a bit more details on the kind of error handling you're looking for? > This is my first time writing into mailing list, hopefully I am doing > everything ok. Indeed you are! -- Best regards, Ivan __ R-package-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-package-devel
