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<p class="MsoPlainText">My $0.02.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Dirk is right - pick something and stick with it, but avoid the raw pointers, especially if your experience is limited. It's much easier to learn the smart pointers std::shared_ptr and std::unique_ptr, or their boost equivalents, rather
than deal with raw pointers in new code.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoNormal"><a href="http://www.codeproject.com/Articles/541067/Cplusplus11-Smart-Pointers">http://www.codeproject.com/Articles/541067/Cplusplus11-Smart-Pointers</a><o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">std::vector is your friend; learn to use it. Just allocate enough space with resize, use operator(...)[] to access/set the elements of the vector (do not use .push_back as this appends to the end of the vector) and you will not suffer
the overhead of extending the size of the vector (some implementations copy the entire vector).<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText"><a href="http://www.codeproject.com/Articles/5378/A-Presentation-of-the-STL-Vector-Container">http://www.codeproject.com/Articles/5378/A-Presentation-of-the-STL-Vector-Container</a><o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoNormal">"After reading this article, the reader should be able to use the vector container effectively and should find no use for dynamic C-style arrays again." In fact, you should learn the Standard Template Library very well as the algorithms
and containers it implements are highly optimized and very efficient.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">I have made good use of Armadillo, have avoided any explicit memory allocation at all, and even append columns to matrices when necessary.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Dale Smith, Ph.D.<o:p></o:p></p>
<p class="MsoPlainText">Senior Financial Quantitative Analyst<o:p></o:p></p>
<p class="MsoPlainText">Risk & Compliance<o:p></o:p></p>
<p class="MsoPlainText">Fiserv<o:p></o:p></p>
<p class="MsoPlainText">Office: 678-375-5315<o:p></o:p></p>
<p class="MsoPlainText">www.fiserv.com<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">-----Original Message-----<br>
From: rcpp-devel-bounces@r-forge.wu-wien.ac.at [mailto:rcpp-devel-bounces@r-forge.wu-wien.ac.at] On Behalf Of Dirk Eddelbuettel<br>
Sent: Tuesday, July 09, 2013 2:46 AM<br>
To: Darren Cook<br>
Cc: rcpp-devel@r-forge.wu-wien.ac.at<br>
Subject: Re: [Rcpp-devel] simple Rcpp function produces: "AddressSanitizer: attempting free on address which was not malloc"</p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">On 9 July 2013 at 11:42, Darren Cook wrote:<o:p></o:p></p>
<p class="MsoPlainText">| > The C++ function, though, is quite simple -- I wonder if anyone
<o:p></o:p></p>
<p class="MsoPlainText">| > might be able to spot easily what is going on?<o:p></o:p></p>
<p class="MsoPlainText">| > ...<o:p></o:p></p>
<p class="MsoPlainText">| > double Cnm;<o:p></o:p></p>
<p class="MsoPlainText">| > Cnm = nChoosek(*n, *m);<o:p></o:p></p>
<p class="MsoPlainText">| > ...<o:p></o:p></p>
<p class="MsoPlainText">| > int* combmat;<o:p></o:p></p>
<p class="MsoPlainText">| > combmat = new int[(int)Cnm**(m+0)];<o:p></o:p></p>
<p class="MsoPlainText">| <o:p></o:p></p>
<p class="MsoPlainText">| I'm not sure if this is the cause of the complaint, but in a code
<o:p></o:p></p>
<p class="MsoPlainText">| review I'd have red flags all over that last line:<o:p></o:p></p>
<p class="MsoPlainText">| <o:p></o:p></p>
<p class="MsoPlainText">| * Cnm is a double, but you truncate it to an int.<o:p></o:p></p>
<p class="MsoPlainText">| Rounding *down* to then do a memory allocation makes me nervous.<o:p></o:p></p>
<p class="MsoPlainText">| If Cnm is only ever an integer, keep it as int and cast the return
<o:p></o:p></p>
<p class="MsoPlainText">| value from nChoosek() instead.<o:p></o:p></p>
<p class="MsoPlainText">| (You also do the same cast to int ncols later on.)<o:p></o:p></p>
<p class="MsoPlainText">| <o:p></o:p></p>
<p class="MsoPlainText">| * Can *(m+0) be rewritten as *m ?<o:p></o:p></p>
<p class="MsoPlainText">| <o:p></o:p></p>
<p class="MsoPlainText">| * I assume it should read: Cnm * nrows<o:p></o:p></p>
<p class="MsoPlainText">| where nrows is *m?<o:p></o:p></p>
<p class="MsoPlainText">| Very minor but ** also means double dereference, so I'd like at
<o:p></o:p></p>
<p class="MsoPlainText">| least a space to make the intention clear.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Adding to this:<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText"> * you use 'new' to allocatate space, but DO NOT call delete -- memory leak.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">In short, these days you almost never ever have a reason to use malloc/free or new/delete. Ever. Learn more about STL vectors, and use those.<o:p></o:p></p>
<p class="MsoPlainText">Safer. Easier. Better.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Pick one representation: arma, or Rcpp, or STL vectors. Stick with it. Maybe develop your core computation in a standalone program on fixed data. The connect to R.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Hth, Dirk<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">| <o:p></o:p></p>
<p class="MsoPlainText">| Darren<o:p></o:p></p>
<p class="MsoPlainText">| <o:p></o:p></p>
<p class="MsoPlainText">| _______________________________________________<o:p></o:p></p>
<p class="MsoPlainText">| Rcpp-devel mailing list<o:p></o:p></p>
<p class="MsoPlainText">| <a href="mailto:Rcpp-devel@lists.r-forge.r-project.org">
<span style="color:windowtext;text-decoration:none">Rcpp-devel@lists.r-forge.r-project.org</span></a><o:p></o:p></p>
<p class="MsoPlainText">| <a href="https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-deve">
<span style="color:windowtext;text-decoration:none">https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-deve</span></a><o:p></o:p></p>
<p class="MsoPlainText">| l<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">--<o:p></o:p></p>
<p class="MsoPlainText">Dirk Eddelbuettel | <a href="mailto:edd@debian.org"><span style="color:windowtext;text-decoration:none">edd@debian.org</span></a> |
<a href="http://dirk.eddelbuettel.com"><span style="color:windowtext;text-decoration:none">http://dirk.eddelbuettel.com</span></a> _______________________________________________<o:p></o:p></p>
<p class="MsoPlainText">Rcpp-devel mailing list<o:p></o:p></p>
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<p class="MsoPlainText"><a href="https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel"><span style="color:windowtext;text-decoration:none">https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel</span></a><o:p></o:p></p>
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