Initializing without assigning

Coming from writing mostly in Java, I have trouble understanding how to
declare a member without initializing it, and do that later... In Java,
I would write something like
public static void main(String[] args) {
 MyType aMember;
 ...
 aMember = new MyType(...)
 ...
}
However, in C++ this does not seem to work. I declare in class (it's
for serial port communication) like this:

#include <fstream>
#include <boost/thread/thread.hpp>

class COMConn {
public:
    COMConn(int port);
    ~COMConn();

    char *send(char);
    char *send(char, char[]);
private:
    void connect(int);

    std::ifstream input;
    std::ofstream output;

    boost::thread inputthread;
    boost::thread outputthread;
};

But when I want to initialize the threads and streams, I want to do
something like

void COMConn::connect(int port) {
 this->input = std::ifstream("COM1:");
 this->inputthread = boost::thread(&input.read); // Not correct, needs
arguments, but skip that for now
 //etc for the others
}

How do you go about doing this in C++? I found that I could do
this->input.open("COM1:");
But that is hardly something that will work in general. I find this
very confusing I must say... Thanks you for any advice