In C++, how to compute the mean of a vector of integers using a vector view and gsl_stats_mean?

my program manipulates STL vectors of integers but, from time to time, I need to calculate a few statistics on them. Therefore I use the GSL functions. To avoid copying the STL vector into a GSL vector, I create a GSL vector view, and give it to the GSL functions, as in this piece of code: ``` #include <iostream> #include <vector> #include <gsl/gsl_vector.h> #include <gsl/gsl_statistics.h> using namespace std; int main( int argc, char* argv[] ) { vector<int> stl_v; for( int i=0; i<5; ++i ) stl_v.push_back( i ); gsl_vector_int_const_view gsl_v = gsl_vector_int_const_view_array( &stl_v[0], stl_v.size() ); for( int i=0; i<stl_v.size(); ++i ) cout << "gsl_v_" << i << "=" << gsl_vector_int_get( &gsl_v.vector, i ) << endl; cout << "mean=" << gsl_stats_mean( (double*) gsl_v.vector.data, 1, stl_v.size() ) << endl; } ``` Once compiled (gcc -lstdc++ -lgsl -lgslcblas test.cpp), this code outputs this: ``` gsl_v_0=0 gsl_v_1=1 gsl_v_2=2 gsl_v_3=3 gsl_v_4=4 mean=5.73266e-310 ``` The vector view is properly created but I don't understand why the mean is wrong (it should be equal to 10/5=2). Any idea? Thanks in advance.