[Rcpp-devel] How to free memory in Rcpp

Honglang Wang wanghonglang2008 at gmail.com
Fri Dec 14 05:07:07 CET 2012

Hi Yan,
Thanks a lot. Your advice is really the point for me. Have a good night.

Best wishes!

Honglang Wang

Office C402 Wells Hall
Department of Statistics and Probability
Michigan State University
1579 I Spartan Village, East Lansing, MI 48823
wangho16 at msu.edu

On Thu, Dec 13, 2012 at 10:54 PM, Yan Zhou <zhouyan at me.com> wrote:

> You really are not reading the list as close as you should be. If you want
> advice, then take it when people give it to you or stop asking.
> AFAIK, your code does not involve manually allocated memory, all memories
> are managed by RAII objects, I don't see where the question of "freeing
> memory" come from. And the error message suggests nothing about memory
> problems. So either you have no idea of C++ at all or you are just asking
> some random question and hope others to debug your code. The later is not
> going to happen.
> On Dec 14, 2012, at 3:25 AM, Honglang Wang <wanghonglang2008 at gmail.com>
> wrote:
> I am sorry that I was abusing this list. My point is
> 1) First, this code works for me for some simulation cases. I repeated the
> simulation 1000 times, which then called this Rcpp function 1000 times at
> least. And this code worked perfectly.
> Computers don't do random things, unlike human beings. Something worked
> once, is very likely to work whatever times you repeat it as long as the
> input is the same (unless the function has side effect). So repeating it
> 1000 times is the same as once.
> 2) But in some other simulation case (here what I mean by simulation case,
> just change some parameters to produce the data, but the data formats are
> the same.), when I repeated the simulation 1000 times, at some point, for
> example, at the 298th simulation, it did not work. Then in order to see
> what is the problem, I just did the 298th simulation separately (since I
> set the seed, it used the same data), but it worked well in this case. Then
> I really have no idea what is going on there.
> Since you already find an input that crash the program, you should go
> through the function to see where exactly the crash happens. For example,
> print out the intermediate steps in both R and C++ side to see where the
> execution stopped. Using a debugger is better. Sometime it takes a great
> time to trace back the crash site. Debugging can be exhausting. But it is
> supposed to be done by YOU. You cannot throw a bunch of code to the list,
> ask a non-sense question, and hope others to spend time to debug it for you.
> Here are a few things people usually do before asking in a mailing list
> (not just Rcpp list, any such lists like R-help, StackOverflow, etc).
> 1. I write a program, it crashes,
> 2. I find out the site of crash
> 3. I make the program simpler and simpler until it is minimal and the
> crash is now reproducible.
> 4. I still cannot figure out what is wrong with that four or five lines
> that crash the minimal example
> 5. I ask
> Ask yourself, have you go through the first 4 steps? It does not matter
> how stupid your questions are. We all asked silly questions before, that is
> how we learn. But it matters you put in effort to ask the right question.
> The more effort you put into it, the more specific question you ask and
> more helpful answers you get. I suspect you don't know how to do that at
> all.  So if I were you, I will take Dirk's advice, take a deep breath, go
> for a walk, and start learning C++.
> Yan
> Best wishes!
> Honglang Wang
> Office C402 Wells Hall
> Department of Statistics and Probability
> Michigan State University
> 1579 I Spartan Village, East Lansing, MI 48823
> wangho16 at msu.edu
> On Thu, Dec 13, 2012 at 10:06 PM, Dirk Eddelbuettel <edd at debian.org>wrote:
>> Honglang,
>> You are now abusing the free facilities offered by this list.  Your
>> examples
>> are not self-contained [ no sample data or simulated data ] and hence not
>> reproducible.  Your code is complex, and not motivated. And we have told
>> you
>> REPEATEDLY to shorten your code to chunks until it works.
>> On 13 December 2012 at 21:15, Honglang Wang wrote:
>> | I have no idea what's this error.
>> My best guess is that we already explained this to you, but you are not
>> really reading our replies all that closely.  Here is a hint: repeatedly
>> calling an R function is probably not the smartest thing to do in an
>> otherwise complex and hard to decipher program. [1]
>> | I am just wondering whether I need to free some memory in this code.
>> You are also making it pretty clear that you don't really know what you
>> are
>> doing with C++, or else you would not ask this question (and the earlier
>> email people were to polite to reply to).
>> I suggest that you take a deep breath, go for a walk and once you're back,
>> start learning about C++.
>> So please stop emailing the list unless you have something more
>> substantial
>> to post or ask -- and follow common courtesy and list etiquette.
>> Right now you are wasting your time, as well as the time of a few hundred
>> list subscribers.  Stop now.
>> Dirk
>> [1] Just to be plain: Calling a function repeatedly is not per se a bad
>> thing.  Complete example below.
>> -----------------------------------------------------------------------------
>> #include <Rcpp.h>
>> using namespace Rcpp;
>> // [[Rcpp::export]]
>> double foo(Function f, NumericVector x) {
>>   double r = 0.0;
>>   for (int i=0; i<100; i++)
>>     r += as<double>(f(x));
>>   return r;
>> }
>> /*** R
>> x <- 1:10
>> foo(mean, x)
>> ***/
>> -----------------------------------------------------------------------------
>> Here is the result from the 100 calls:
>> R> sourceCpp("/tmp/fun.cpp")
>> R> x <- 1:10
>> R> foo(mean, x)
>> [1] 550
>> R>
>> As expected...
>> --
>> Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com
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