Trouble compiling c++ examples that read .mat files on osx

When compiling one of the examples for reading mat files in c++ I get the following result

 bash-3.2$ gcc -I /Applications/MATLAB_R2012a.app/extern/include/ matdgns.c  
 matdgns.c: In function 'diagnose':
 matdgns.c:81: warning: format '%d' expects type 'int', but argument 3 has type 'mwSize'
 matdgns.c:81: warning: format '%d' expects type 'int', but argument 3 has type 'mwSize'
 matdgns.c:112: warning: format '%d' expects type 'int', but argument 3 has type 'mwSize'
 matdgns.c:112: warning: format '%d' expects type 'int', but argument 3 has type 'mwSize'
 Undefined symbols for architecture x86_64:
 "_matOpen", referenced from:
  _diagnose in ccAC9eU9.o
 "_matGetDir", referenced from:
 _diagnose in ccAC9eU9.o
 "_mxFree", referenced from:
        _diagnose in ccAC9eU9.o
    "_matClose", referenced from:
        _diagnose in ccAC9eU9.o
    "_matGetNextVariableInfo", referenced from:
        _diagnose in ccAC9eU9.o
    "_mxGetNumberOfDimensions_730", referenced from:
        _diagnose in ccAC9eU9.o
    "_mxIsFromGlobalWS", referenced from:
        _diagnose in ccAC9eU9.o
    "_mxDestroyArray", referenced from:
        _diagnose in ccAC9eU9.o
    "_matGetNextVariable", referenced from:
        _diagnose in ccAC9eU9.o
 ld: symbol(s) not found for architecture x86_64
 collect2: ld returned 1 exit status

So it looks like the linker just can't find the libmat.dylib library, but I have set up my environment as described in http://www.mathworks.com/help/techdoc/matlab_external/f19027.html so the command "echo $DYLD_LIBRARY_PATH" results in

 bash-3.2$ echo $DYLD_LIBRARY_PATH
 /Applications/MATLAB_R2012a.app/bin/maci64:/Applications/MATLAB_R2012a.app/sys/os/maci64:/Applications/MATLAB_R2012a.app/bin/maci64:

Can anyone see what I'm missing?

Answer 1

[Ken Atwell]

The doc you indicated assumes you are building from within MATLAB, using the MEX command. You're building with GCC from the command-line. You need to include the MATLAB libraries on your command line (MEX does this for you). Include the following in your gcc invocation:

 -lmx -lmex -lmat

This may be enough. If not, trying building your engine application with "mex" inside MATLAB. Use the -v switch to get verbose output, which will help you determine the exact gcc command line(s) needed to build outside of MATLAB.

[Craig]

Thanks for the start, I just needed to add the -lmx and -lmat and -L/Applications/MATLAB_R2012a.app/bin/maci64/ as explained on http://www.alecjacobson.com/weblog/?p=924