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jeanluct / braidlab

Matlab package for analyzing data using braids
GNU General Public License v3.0
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Specifying a compiler for MEX #115

Closed jeanluct closed 9 years ago

jeanluct commented 9 years ago

What a pain: the instructions in the guide, e.g. make CC=gcc-4.7 CXX=g++-4.7, do not work as intended. It seemed to work on my system, but when trying on Alex F's Ubuntu 14.10 there was a problem: since 14.10 uses GCC-4.9 by default, mex can't support it.

The problem is that the CXX= settings are not passed to MEX. So how are we supposed to specify a compiler for MEX? Mystifying... (hello issue #67...).

jeanluct commented 9 years ago

This page has the helpful line about mex -setup: "If you have multiple compilers, MATLAB displays a message with links to set up a different compiler." Except it doesn't:

$ mex -setup

MEX configured to use 'gcc' for C language compilation.
Warning: The MATLAB C and Fortran API has changed to support MATLAB
     variables with more than 2^32-1 elements. In the near future
     you will be required to update your code to utilize the
     new API. You can find more information about this at:
     http://www.mathworks.com/help/matlab/matlab_external/upgrading-mex-files-to-use-64-bit-api.html.

To choose a different language, execute one from the following:
 mex -setup C++ 
 mex -setup FORTRAN

How are we supposed to tell MEX about the different compilers we have?

mbudisic commented 9 years ago

(Continuing discussion, not providing a solution) From inside MATLAB, configurations for different (supported) compilers can be read using mex.getcompilerconfigurations http://www.mathworks.com/help/matlab/ref/mex.getcompilerconfigurations.html

For example, on my system:

>> a = mex.getCompilerConfigurations('C','Supported').Details

a = 

  CompilerConfigurationDetails with properties:

         CompilerExecutable: '/usr/bin/xcrun -sdk macosx10.9 clang'
              CompilerFlags: '-fno-common -arch x86_64 -mmacosx-version-min=10.9 -fexceptions -isysro...'
          OptimizationFlags: '-O2 -DNDEBUG'
                 DebugFlags: '-g'
           LinkerExecutable: ''
                LinkerFlags: ''
    LinkerOptimizationFlags: '-O'
           LinkerDebugFlags: '-g'
                     SetEnv: 'CC="/usr/bin/xcrun -sdk macosx10.9 clang"
CXX="/usr/bin/xcrun -sdk maco...'
           CommandLineShell: ''
        CommandLineShellArg: ''

Configurations scripts for different compilers are stored in xml files that on my computer reside in:

/Applications/MATLAB_R2014b.app/bin/maci64/mexopts/

I guess if we wanted to run a different compiler, we would generate an xml file like this and pass it to mex using -f option. I haven't tried it, though.

mbudisic commented 9 years ago

Sorry about that, writing in a hurry. I added more detail now.

Did Alex try setting global variable, via export or setenv as well?

jeanluct commented 9 years ago

Yeah, I was looking at those XML files. Seems a pain and hard to describe in the guide.

We tried setting CXX globally, no help.

mbudisic commented 9 years ago

Did you try using update-alternatives on linux for less painful switching of compilers? http://lektiondestages.blogspot.com/2013/05/installing-and-switching-gccg-versions.html

jeanluct commented 9 years ago

Changing the XML file doesn't seem to work...

Maybe alternatives is the way to go, but it's a pain to describe in the guide.

jeanluct commented 9 years ago

Script and updated guide in 622d50c. Not very satisfying: the script devel/gcc-alternatives basically sets things up automatically, as long as it's GCC 4.x. This script is not distributed formally with braidlab and I put it under devel for convenience.

jeanluct commented 9 years ago

Ok, Alex F was able to compile on Ubuntu 14.10 with Matlab 2014a following the guide, so this seems fixed enough.