[Rcpp-devel] simple Rcpp function produces: "AddressSanitizer: attempting free on address which was not malloc"

[Dirk Eddelbuettel]

On 9 July 2013 at 11:42, Darren Cook wrote:
| > The C++ function, though, is quite simple -- I wonder if anyone might be
| > able to spot easily what is going on?
| > ...
| >     double Cnm;
| >     Cnm = nChoosek(*n, *m);
| >     ...
| >     int* combmat;
| >     combmat = new int[(int)Cnm**(m+0)];
| 
| I'm not sure if this is the cause of the complaint, but in a code review
| I'd have red flags all over that last line:
| 
|   * Cnm is a double, but you truncate it to an int.
|     Rounding *down* to then do a memory allocation makes me nervous.
|     If Cnm is only ever an integer, keep it as int and cast the return
| value from nChoosek() instead.
|     (You also do the same cast to int ncols later on.)
| 
|   * Can  *(m+0) be rewritten as *m ?
| 
|   * I assume it should read:   Cnm * nrows
|     where nrows is *m?
|     Very minor but ** also means double dereference, so I'd like at
| least a space to make the intention clear.

Adding to this:

    * you use 'new' to allocatate space, but DO NOT call delete -- memory leak.

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.
Safer. Easier. Better.

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.

Hth,  Dirk

| 
| Darren
| 
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-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com