Calling MATLAB from a C++ program in Linux

Hi there,

I'm trying to call the MATLAB engine from some C++ which I'm writing. I'm using Debian 6.0.4 64 bit. GCC version is 4.4.5-8.

In order to test out what the built in engine can do, I thought a good place to start would be to compile one of the demos which comes with MATLAB (in this case, engdemo.cpp).

I've install csh and when I call g++ engdemo.cpp, these are the errors I get:

% g++ engdemo.cpp
/tmp/ccD4qsD5.o: In function `main':
engdemo.cpp:(.text+0xa8): undefined reference to `engOpen'
engdemo.cpp:(.text+0xf4): undefined reference to `mxCreateDoubleMatrix'
engdemo.cpp:(.text+0x104): undefined reference to `mxGetPr'
engdemo.cpp:(.text+0x12d): undefined reference to `engPutVariable'
engdemo.cpp:(.text+0x13e): undefined reference to `engEvalString'
engdemo.cpp:(.text+0x14f): undefined reference to `engEvalString'
engdemo.cpp:(.text+0x160): undefined reference to `engEvalString'
engdemo.cpp:(.text+0x171): undefined reference to `engEvalString'
engdemo.cpp:(.text+0x182): undefined reference to `engEvalString'
engdemo.cpp:(.text+0x1b1): undefined reference to `mxDestroyArray'
engdemo.cpp:(.text+0x1c2): undefined reference to `engEvalString'
engdemo.cpp:(.text+0x1e1): undefined reference to `engOutputBuffer'
engdemo.cpp:(.text+0x24e): undefined reference to `engEvalString'
engdemo.cpp:(.text+0x282): undefined reference to `engGetVariable'
engdemo.cpp:(.text+0x2aa): undefined reference to `mxGetClassName'
engdemo.cpp:(.text+0x2e2): undefined reference to `mxDestroyArray'
engdemo.cpp:(.text+0x2ee): undefined reference to `engClose'
collect2: ld returned 1 exit status

Now there seem to be a number of guides on the internet explaining how to set it up. Some make mention of makefiles, but I haven't implemented one as it doesn't actually explain what to do.

Any help you can provide would be greatly appreciated!

Many thanks!

Answer 1

[Ken Atwell]

gcc/g++ is not able to find MATLAB's header and library files. If compiling from a Linux shell, you will need to add -I, -L, and -l switches (and maybe others) to get a successfully compilation and linkage.

You may find it easier to start by compiling with mex within MATLAB ( starting point for using -f to build engine files). Once that is working, if you really want to compile from the shell, invoke mex with the -v (verbose) flag to learn the exact switches that mex passes down to gcc, and then use those same switches within your shell invocation.

[J]

Hi Ken,

Thank you for your help.

So can I just check what the difference between mex and the MATLAB engine is? I think I misunderstood what mex does- so does it compile c or cpp files like a shell does, but invoke the gcc/g++ compiler from within it?

Many thanks!

[Ken Atwell]

The term "mex" can refer to both a MEX-File (a compiled plug-in to MATLAB -- not what you are using) and the MATLAB tool for compiling both MEX-Files and MATLAB Engine files.

The "mex" command in MATLAB essentially invokes gcc (on Linux) with the right command-line parameters to successfully compile a MEX-File or a MATLAB Engine file. Invoking "mex" with the -v switch will give you more information about what exactly MEX is doing behind the scenes, should you eventually want to compile from the Linux shell instead of MATLAB. That said, you may find is easier to alway compile with the mex command in MATLAB, which handles the details behind getting the right command line to the compiler.

[Tung Nguyen]

I did a video explaining how I got it to work on the R2013a version of Linux.

https://www.youtube.com/watch?v=iuOTf7mTooE

Best of luck