I put together this code after looking at some other code here:
Code:
class Thing
{
private:
    int x;
public:
    Thing();
    Thing(int);
    void set(int);
    friend Thing operator +(const Thing&, const Thing&);
    friend ostream operator <<(const ostream&, const Thing&);
};
I get this error on the bold line:

c:\cpp\oper\thing.h(12) : fatal error C1001: INTERNAL COMPILER ERROR
(compiler file 'msc1.cpp', line 1786)
Please choose the Technical Support command on the Visual C++
Help menu, or open the Technical Support help file for more information
Error executing cl.exe.

What does that mean?