[Rd] Question on parsing R code from C

[Simon Urbanek]

On Nov 16, 2011, at 2:48 PM, KR wrote:

> Simon Urbanek <simon.urbanek <at> r-project.org> writes:
>> Not without seeing the actual code. (And details such as which platform you're 
> on).
>> Note that setup_Rmainloop() is the last to set the SETJMP context target so 
> you should make sure the stack is
>> still present after it finished (i.e. you can't call it from a sub-function - 
> which Rf_initEmbeddedR
>> does) otherwise error without an enclosing context will crash. Or to put it 
> other way round, create a
>> context around your parse/eval code (probably the easiest way to do that is to 
> use R_ToplevelExec).
> 
> I will try to produce the exact code I am using (at the moment it embedded in
> other code you would not be interested in), platforms are Windows XP and
> Windows7-64. Some points:
> 
> 1. Actually R_tryEvalSilent (and R_tryEval) calls R_ToplevelExec.

Yes, but that's not where you get the crash.


> Moreover if 
> the problem is linked to the SETJMP (which I do not know much about 
> unfortunately, my background is C++) it's my understanding that it should 
> manifest itself even for other parse and evaluation errors. Instead the problem
> arise if and only if I pass a wrongly escaped string. I.e. rnorm(10a10) does not 
> result in a crash.
> Is the R code doing something differently in this specific case?
> 

Your crash is in the parsing step, not in the evaluator (if I understand you correctly) and the parsing step is not wrapped in a context - that's my guess based on what you told us.

Cheers,
Simon


> 2. My code is almost exactly the same as:
> http://stackoverflow.com/questions/2463437/r-from-c-simplest-possible-
> helloworld/2464479#2464479
> skipping the EXAMPLE 1 part and passing the capture.output(eval(parse(text="
> <code>"))) string to R_tryEval in EXAMPLE 2.
> 
> Cheers,
> 
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