Question

I’m trying to update a project which uses SWIG to build an interface from ruby to matlab. The matlab C-API has changed and now I get the following error at runtime.

`mxCreateDoubleMatrix_730′: Expected argument 0 of type mwSize, but got Fixnum 20 (TypeError)

I found mwSize defined in tmwtypes.h, which was not being included in the SWIG interface file:

tmwtypes.h:typedef int mwSize;
tmwtypes.h:typedef size_t    mwSize;         /* unsigned pointer-width integer */

But, if I add tmwtypes.h to the include section of the SWIG interface, I still get the TypeError and if I add it to both the include and the parse section, I get the following compile error:

Error: CPP #error “”This code must be compiled using a 2’s complement representation for signed integer values””. Use the -cpperraswarn option to continue swig processing.

Giving up on tmwtypes.h, my solution is to add the following to the SWIG interface file.

%typemap(in) mwSize {
   $1 = NUM2INT($input);
}

You can look at the complete SWIG interface file at:
https://github.com/morrifeldman/matlab-ruby/blob/master/ext/matlab_api/matlab_api.i

After adding this typemap, the program compiles and seems to work perfectly.

I have two related questions I would like answered:

1. Is the correct solution to the TypeError I am having with mwSize. Should I try something else instead?

2. I thought that including tmwtypes.h would fix my problem. Why didn’t it work?

For reference, I’m using OSX Mountain Lion with Xcode 4.5.2. The Makefile is calling gcc-4.2. ‘gcc-4.2 –version’ gives ‘i686-apple-darwin11-llvm-gcc-4.2 (GCC) 4.2.1’

Thanks!

Answer 1

I was able to replace the typemap with:

typedef size_t    mwSize;

However, I can’t offer any insight into what is going on.