Problems building with G++ on MATLAB

Question

I'm a bit new to MATLAB but am currently trying to build MEX files using G++ (version 6.3) as the compiler. I got this error

MEX completed successfully.
Building with 'g++'.
Error using mex
/disks/local/sceneflow2/./external/libtrws/trwsMex.cpp:14:13: error: conflicting declaration ‘typedef
int mwSize’
In file included from /usr/local/MATLAB/R2016a/extern/include/matrix.h:25:0,
                 from /usr/local/MATLAB/R2016a/extern/include/mex.h:51,
                 from /disks/local/sceneflow2/./external/libtrws/trwsMex.cpp:9:
/usr/local/MATLAB/R2016a/extern/include/tmwtypes.h:795:19: error: ‘mwSize’ has a previous
declaration as ‘typedef size_t mwSize’
/disks/local/sceneflow2/./external/libtrws/trwsMex.cpp:15:13: error: conflicting declaration ‘typedef
int mwIndex’
In file included from /usr/local/MATLAB/R2016a/extern/include/matrix.h:25:0,
                 from /usr/local/MATLAB/R2016a/extern/include/mex.h:51,
                 from /disks/local/sceneflow2/./external/libtrws/trwsMex.cpp:9:
/usr/local/MATLAB/R2016a/extern/include/tmwtypes.h:796:19: error: ‘mwIndex’ has a previous
declaration as ‘typedef size_t mwIndex’


Error in make_mex (line 20)
mex ./external/libtrws/trwsMex.cpp -largeArrayDims CXXFLAGS="\$CXXFLAGS -std=c++0x -fpermissive"
-outdir build

I don't get it. Why is /usr/local/MATLAB/R2016a/extern/include/tmwtypes.h definition of mwSize conflicting with /usr/local/MATLAB/R2016a/extern/include/mex.h ? Aren't they predefined libraries included with MATLAB (meaning they should work fine?)

By the way, /disks/local/sceneflow2/./external/libtrws/trwsMex.cpp has a line which includes the aforementioned mex.h .

Answer 1

The error message has to blocks (for two different errors), let's look at the first one only. I've split it out into three "lines":

 /disks/local/sceneflow2/./external/libtrws/trwsMex.cpp:14:13: error: conflicting declaration 'typedef int mwSize' In file included from /usr/local/MATLAB/R2016a/extern/include/matrix.h:25:0, from /usr/local/MATLAB/R2016a/extern/include/mex.h:51, from /disks/local/sceneflow2/./external/libtrws/trwsMex.cpp:9: /usr/local/MATLAB/R2016a/extern/include/tmwtypes.h:795:19: error: 'mwSize' has a previous declaration as 'typedef size_t mwSize' 

The first line says that the compiler found a declaration for mwSize on line 14 of your trwsMex.cpp file, where it says typedef int mwSize .

The last line says that this mwSize was already defined in the tmwtypes.h header that comes with MATLAB.

The second line says that this header file was included by matrix.h , which is included by mex.h , which is included by your trwsMex.cpp on line 9.

---

So, to fix the error, don't define mwSize and mwIndex in your MEX-file source code, these are defined by MATLAB's headers.