undefined reference to Class::Class(std::vector<double, std::allocator<double> >)

std::vector<double>

std::vector<double, std::allocator<double> >

std::vector<double> x1;
std::vector<double> x2;
std::vector<double> myvec;
double thisX;

for (int i=0; i<x1.size(); i++ {
    thisX = x1[i];
    myvec.push_back(thisX);
}
for (int i=0; i<x2.size(); i++ {
    thisX = x2[i];
    myvec.push_back(thisX);
}

Class MyClass( myvec );
// has a constructor for std::vector<double>
// compiler throws the undefined reference to
// Class::Class(std::vector<double, std::allocator<double> >)