Another "undefined reference" error when linking boost libraries

Question

I've seen several other posts that deal with this exact same issue. However, none of their solutions seem to work for me. I am compiling the following code:

#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/io.hpp>
#include <boost/timer/timer.hpp>

using namespace boost::numeric::ublas;

int main(){    
   matrix<double> mat1 (3,3);
   matrix<double> mat2 (3,3);
   matrix<double> mat3 (3,3);

   unsigned k=0;

   for(unsigned i = 0; i < mat1.size1(); ++i){
      for(unsigned j = 0; j < mat1.size2(); ++j){
         mat1(i,j) = k;
         mat2(i,j) = 2*k++;
      }   
   }   

   k=0;
   if(1){
      boost::timer::auto_cpu_timer t;
      while(k<1000){
         mat3 = prod(mat1,mat2);
         k++;
      }   
   }   
   return 0;
}

I am compiling from the command line using:

$ g++ matrix_test.cpp -o matrix_test -lboost_system -lboost_timer

and receiving the following error:

usr/lib/gcc/i686-redhat-linux/4.7.0/../../../libboost_timer.so: undefined reference to `boost::chrono::steady_clock::now()'
collect2: error: ld returned 1 exit status

If I add -lboost_chrono when I compile, I get this error:

/usr/lib/gcc/i686-redhat-linux/4.7.0/../../../libboost_chrono.so: undefined reference to `clock_gettime'
collect2: error: ld returned 1 exit status

I can trace clock_gettime to sys/time.h. Unfortunately, I cannot find a corresponding .so file to link to. What am I missing here?

Answer 1

You must add -lrt to your link libraries

g++ matrix_test.cpp -o matrix_test -lboost_system -lboost_timer -lboost_chrono -lrt

---

Update (2016-08-31)

This still seems to be an issue. When you lookup man clock_gettime, this leads to the solution (-lrt), but it also says

Link with -lrt (only for glibc versions before 2.17).

So when your glibc is newer, your problem might be something else.

Answer 2

Add -lrt to your g++ invocation – clock_gettime is in librt.so.