Mex compilation of vl_nnconv.nu failed about matconvnet HOT 3 CLOSED

Hi, this is old known issue with Matlab in Linux. As it is distributed as a binary blob, it is usually compiled with a GCC which Mathworks decides to use (usually much older than the one distributed in Ubuntu's LTS releases, usually so old that it's not even in repositories among the older gcc version). Main problem arises especially with libstdc++ library as Matlab is distributed with its own version, therefore anything written in C++ and compiled in system (newer) version of GCC is not able to link in Matlab by default. That is why mathworks sets the compiler to be the recommended version (in this case to gcc-4.4).
However there are other solutions than compiling it's own version of GCC. First thing is to set proper version of gcc, which you can usually do by 'mex -setup' and then check the settings in ~/.matlab/<version>/mexopts.sh. I usually set it just to gcc or g++ without a version specification.
Then it is possible to force Matlab to link against the system version of libstdc++ by using the LD_PRELOAD trick, e.g. by running Matlab with:

LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libstdc++.so.6 matlab

This is sort of dirty solution too, but to me it has shown to be the most versatile as then you can run any system commands written in C++ in Matlab without getting linker error.
I hope that someone will find it useful, maybe in the future :)

from matconvnet.

SOLVED !
I had to do a pretty drastic fix. I installed the older version of gcc(i.e. gcc-4.4) alongside the existing version by following the instructions here : http://xlcwu.wordpress.com/2012/07/24/ubuntu-12-04-gcc-4-4/
The instructions also specify how to make gcc-4.4 the default compiler. Then, in MATLAB, I ran
mex -setup
and chose option 1(create mexopts.sh) file in my home directory. I edited the mexopts.sh file as described in http://stackoverflow.com/questions/8524235/how-to-provide-matlab-with-the-old-gcc-version-it-wants

Voila ! The compilation went through. I am not too happy with the fact that I changed the default version from my current(gcc-4.8) to 4.4 but whatever !

from matconvnet.

On another machine, I installed gcc-4.4 and modified mexopts.sh to use gcc-4.4. That worked as well. I did not have to resort to LD_PRELOAD trick. Good to know, though.

from matconvnet.