Re: How to pass two dimensional arrays to C

[Jeffrey Creem <jeff@thecreems.com>]

Jerry wrote:
> In my project to write a binding for a popular plotter written in C,
> I've hit a brick wall and the problem might be associated with passing
> two-dimensionaal arrays to C. I'm using GNAT on OS X and Xcode. I can
> pass one-dimensional arrays OK. Here are the pertinent parts from an
> example where the problem happens:
> 
> 
>       The C
> 
> 
> typedef double PLFLT;
> typedef int PLINT;
> 
> void c_plmesh(PLFLT *x, PLFLT *y, PLFLT **z, PLINT nx, PLINT ny, PLINT
> opt);
> 
> 
> 
>       The Ada
> 
> 
> type Long_Float_Array_1D is array (Integer range <>) of Long_Float;
> type Long_Float_Array_2D is array (Integer range <>, integer range <>)
> of Long_Float;
> 
> subtype PLINT  is Integer;
> 
> subtype PL_Float_Array    is Long_Float_Array_1D;
> subtype PL_Float_Array_2D is Long_Float_Array_2D;
> 
> procedure plmesh(
>     x   : PL_Float_Array;
>     y   : PL_Float_Array;
>     z   : PL_Float_Array_2D;
>     nx  : PLINT;
>     ny  : PLINT;
>     opt : PLINT);
> pragma Import(C, plmesh, "c_plmesh");
> 
> 
> 
>       And the Ugly
> 
> 
> AdaPLplotProject has exited due to signal 11 (SIGSEGV).
> 
> This appears during the call to plmesh. Any ideas? 
> 
> Thanks,
> Jerry
> 


Perhaps the C code is not really expecting a two dimensional array but 
rather an array of pointers to arrays.

You could try using some of the in progress/alpha swig work (only in SVN 
at the moment at gnuada.sf.net) to autogenerate some bindings to the 
plplot library since plplot appears to come with a SWIG compatible input 
file.

http://plplot.cvs.sourceforge.net/plplot/plplot/bindings/swig-support/

Even if you decide that the swig stuff is not workable yet, perhaps the 
bindings it creates will be enough to give you a hint as to what the 
real structure is here.