Need help allocating space for vector within class definition using boost.

Question

I am trying to allocate space for a boost vector type in a class definition. I am not a good c++ programmer, but shown below is my best attempt. There are no error messages, but when I try to access the vector from my main function it believes that the vector has zero elements. I know this is because I did not tell the compiler how much space to allot when I declared the vector in the class definition, but I do not know how to do this without getting an error. I tried to circumvent this by telling it how big I wanted it in the constructor, but I know the compiler treats this as a redefinition that does not exist outside of the scope of the constructor. Can someone lead me in the right direction? Thanks in advance.

namespace ublas = boost::numeric::ublas;

class Phase
{
 ublas::vector<cdouble> lam;
public:
 // Constructor:
 Phase()
 {
  ublas::vector<cdouble> lam(2);

  for(int i = 0; i < 2; i++)
  {
   lam(i) = 1.0;
  }
 }
 // Destructor:
 ~Phase() {}
 // Accessor Function:
 ublas::vector<cdouble> get_lam() { return lam; }
};

Answer 1

In your constructor you are creating a local variable lam that shadows the class variable lam. You want to initialize the vector in the constructor's initialization list:

Phase() : lam(2)
{
 for(int i = 0; i < 2; i++)
 {
  lam(i) = 1.0;
 }
}

This calls the vector constructor you want as the class is being initialized, instead of the default constructor for the class.