Cpp compilation from python fail but not in the shell

Question

I have a cpp file that compiles fine with g++ by using the shell:

extern "C"{
  #include <quadmath.h>
}

inline char* print( const __float128& val)
{
  char* buffer = new char[128];
  quadmath_snprintf(buffer,128,"%+.34Qe", val);
  return buffer;
}
int main(){
    __float128 a = 1.0;
    print(a);
    return 0;
}

However, when I try to compile it via a python scrit, it fails with the following error:

"undefined reference to quadmath_snprintf"

Here the code of the python script:

import commands
import string
import os
(status, output) = commands.getstatusoutput("(g++ test/*.c -O3 -lquadmath -m64)")

Any idea how to solve this? Thanks.

Probably you don't have LIBRARY_PATH correctly set from python. Try use -L on g++ or export LIBRARY_PATH first. — David Isla
– David Isla, Commented Oct 5, 2016 at 8:05

midor · Accepted Answer · 2016-10-05 08:21:28Z

3

When you open a shell a whole of stuff is silently initialized for you, and most important for your issue, environment variables are set. What you most likely miss is the definition of LIBRARY_PATH, which is the variable used by the linker to look for libraries matching the ones you instruct it to link using the -lNAME flags.

What the linker needs is a list of directories where it will search for files matching libNAME.{a,so}. You can also pass these directories directly using the -L flag, but in general, you should probably try to use a program like CMake, Make or any other build tool.

This will give you access to commands like find_package and target_link_libraries (CMake), to find, respectively add libraries to your build targets, instead of having to maintain your python to compile your stuff.

edited Oct 5, 2016 at 8:21

answered Oct 5, 2016 at 8:16

midor

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2 Comments

David Isla Over a year ago

-L option is looking for LIBRARY_PATH, not LD_LIBRARY_PATH (that's for runtime). Fix your answer please.

David Isla Over a year ago

I made the same mistake! ;) +1

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