R devel - Mar 2012 - Dealing with printf() &c. in third-party library code

Dear all,

I recognise the reason for strongly discouraging use of printf() and
similar C functions in R packages, but I wonder what people do in
practice about third-party code which may be littered with such calls.
I maintain a package (RNiftyReg) which provides an R interface to a
third-party library which contains hundreds of calls to printf(...),
fprintf(stderr,...) and similar. It seems to me that there are several
possible approaches, but all have their issues:

1. Replace all such calls with equivalent Rprintf() calls, using
compiler preprocessing directives to ensure the library does not
become incompatible with other code. For example,

#ifdef RNIFTYREG
Rprintf(...);
#else
printf(...);
#endif

This will be very time-consuming if there are lots of calls, and also
makes the code very untidy and much harder to update when a new
version of the upstream library is released.

2. Remove all such calls from the code altogether, or comment them
out. The problem here is that doing this safely is hard, because the
call could be part of an "if" statement or similar. For example,

if (test)
 printf("Something");
do_something_important;

If the middle line here is removed, then the last line becomes
(erroneously) conditioned on the test. Plus, once again, you are
introducing a lot of small changes to the library itself.

3. Redefine printf to use Rprintf, viz.

#ifdef RNIFTYREG
#include <R.h>
#define printf Rprintf
#endif

This will compile as long as the R function is a drop-in replacement
for the original function, which I believe is true for Rprintf (vs.
printf), but isn't true for Calloc (vs. calloc), for example. And I'm
not sure whether this approach can be used to deal with cases of the
form fprintf(stderr,...), where stderr would need to be redefined.
This approach requires only modest changes to the library itself, but
may be fragile to future changes in R.

Are there any other (better?) alternatives? Any thoughts or advice
would be appreciated.

All the best,
Jon

On 03/14/2012 05:15 AM, Jon Clayden wrote:
> Dear all,
>
> I recognise the reason for strongly discouraging use of printf() and
> similar C functions in R packages, but I wonder what people do in
> practice about third-party code which may be littered with such calls.
> I maintain a package (RNiftyReg) which provides an R interface to a
> third-party library which contains hundreds of calls to printf(...),
> fprintf(stderr,...) and similar. It seems to me that there are several
> possible approaches, but all have their issues:
>
> 1. Replace all such calls with equivalent Rprintf() calls, using
> compiler preprocessing directives to ensure the library does not
> become incompatible with other code. For example,
>
> #ifdef RNIFTYREG
> Rprintf(...);
> #else
> printf(...);
> #endif
>
> This will be very time-consuming if there are lots of calls, and also
> makes the code very untidy and much harder to update when a new
> version of the upstream library is released.
>
> 2. Remove all such calls from the code altogether, or comment them
> out. The problem here is that doing this safely is hard, because the
> call could be part of an "if" statement or similar. For example,
>
> if (test)
>   printf("Something");
> do_something_important;
>
> If the middle line here is removed, then the last line becomes
> (erroneously) conditioned on the test. Plus, once again, you are
> introducing a lot of small changes to the library itself.
>
> 3. Redefine printf to use Rprintf, viz.
>
> #ifdef RNIFTYREG
> #include<R.h>
> #define printf Rprintf
> #endif
>
> This will compile as long as the R function is a drop-in replacement
> for the original function, which I believe is true for Rprintf (vs.
> printf), but isn't true for Calloc (vs. calloc), for example. And
I'm
> not sure whether this approach can be used to deal with cases of the
> form fprintf(stderr,...), where stderr would need to be redefined.
> This approach requires only modest changes to the library itself, but
> may be fragile to future changes in R.
>
> Are there any other (better?) alternatives? Any thoughts or advice
> would be appreciated.
In Makevars, I add -Dfprintf=my_fprintf to the pre-processor flags and 
then implement my_fprintf in a separate source file. This means that the 
source code of the 3rd party library is not touched, and there is some 
scope for re-mapping or otherwise intercepting function arguments. For 
abort and error, I throw an error that encourages the user to save and 
quit immediately, though this is far from ideal. I too would be 
interested in better practices for dealing with this, short of 
whole-sale modification of the third-party library.

Martin
>
> All the best,
> Jon
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

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