[Rcpp-devel] Compiler error I can't understand

[Romain Francois]

Hi,

Without seeing the actual code, it looks like a candidate for 
const_cast. See for example: 
http://www.cplusplus.com/doc/tutorial/typecasting/

If you indeed create a stripped down example, I'll look into it.

Romain

Le 08/05/10 00:20, Douglas Bates a écrit :
>
> The lme4a package (available only from R-forge at present) uses
> facilities from the Matrix package and Rcpp.  The Matrix package
> itself uses the CHOLMOD sparse matrix package written in C.  In the C
> code the sparse matrix representations are defined as structs and
> passed as pointers to such structs.  In lme4a I have source files
> MatrixNs.h and MatrixNs.cpp that provide thin class wrappers around
> these structs.  So the Matrix package header files define
>
> #ifdef __cplusplus
> #extern "C" {
> #endif
>
> typedef struct cholmod_sparse_struct {
>    /* various members */
> } cholmod_sparse;
>
> typedef struct cholmod_common_struct {
>   /* various members */
> } cholmod_common;
>
> typedef cholmod_sparse *CHM_SP;
> typedef cholmod_common *CHM_CM;
>
> CHM_SP M_cholmod_transpose(const CHM_SP, int, CHM_CM);
>
> #ifdef __cplusplus
> }
> #endif
>
> In MatrixNs.h I declare
>
> cholmod_common c;
> class chmSp : cholmod_sparse {
> public:
>     chmSp(Rcpp::S4);
>     CHM_SP transpose(int) const;
> }
>
> with the definition in MatrixNs.cpp of
>
> CHM_SP chmSp::transpose(int values) const {
>     return M_cholmod_transpose(this, values,&c);
> }
>
> and consistently get it thrown back at me by the compiler because of
> an illegal transformation from "const cholmod_sparse*" to
> "cholmod_sparse*" in the line where I call M_cholmod_transpose.
>
> This is severely impeding the development of the code because I can't
> pass chmSp objects as const chmSp&  (or, apparently equivalently, chmSp
> const&) which could cause a lot of unnecessary copying.  Of course,
> those sparse matrices are members of larger objects, etc. and right
> now there is the possibility that everything is being copied
> unnecessarily.
>
> Should this be happening and if so, why?  I believe that the
> declaration of M_cholmod_transpose in effect for this piece of code
> has the first argument declared as const CHM_SP.  (As I said, the
> original code did not have const in the declaration and I may have
> only modified one of the declarations and somehow it is picking up
> another.  As a last resort I have copied all the relevant files from
> the Matrix installed package area to the lme4a source area in my local
> copy just so I am certain of the declaration that is in effect.)
>
> Is there something peculiar about using the wrapper class in the sense
> that "this" is a pointer to a chmSp and I am using it as a
> cholmod_sparse pointer?  Alternatively, is it something about using
> the "this" pointer itself?
>
> The compiler errors are of the form
>
> MatrixNs.cpp: In member function ‘cholmod_sparse*
> MatrixNs::chmSp::transpose(int) const’:
> MatrixNs.cpp:286: error: invalid conversion from ‘const
> cholmod_sparse*’ to ‘cholmod_sparse*’
>
> Any suggestions would be gratefully accepted - especially if they
> solve the problem :-)
>
> If someone wants to look at the actual source files I will try to
> create a stripped down example.  The version on R-forge doesn't show
> exactly this structure because I don't want to leave a version up
> there that doesn't compile.
> _______________________________________________
> Rcpp-devel mailing list
> Rcpp-devel at lists.r-forge.r-project.org
> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
>
>


-- 
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr
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