If condition Checking for Cout

Question

I read this line and I don't understand what it does:

if(cout<<X) //What does this mean? 
{
...
}

Answer 1

It writes X to cout and checks to see if the stream is still in a good state. It is the same as

cout << X;
if (cout) {
   // ....
}

This works because the result of stream << value is a reference to the stream. This is also why you can do things like

stream << x << y << z;

since it is the same as

((stream << x) << y) << z;

Answer 2

In C++, the iostream insertion and extraction operators << and >> return the object on which they were invoked (i.e. their left-hand argument). So if(cout<<X) first inserts X into the cout stream, then uses that stream as a conditional. And iostreams, when tested as booleans, report their status: true if OK, false if in an error state.

So the whole thing means "Print X and then run the following code if cout has no error."