Assigning cout to a variable name

In ANSI C++, how can I assign the cout stream to a variable name? What I want to do is, if the user has specified an output file name, I send output there, otherwise, send it to the screen. So something like:

ofstream outFile;
if (outFileRequested) 
    outFile.open("foo.txt", ios::out);
else
    outFile = cout;  // Will not compile because outFile does not have an 
                     // assignment operator

outFile << "whatever" << endl;

I tried doing this as a Macro function as well:

#define OUTPUT outFileRequested?outFile:cout

OUTPUT << "whatever" << endl;

But that gave me a compiler error as well.

I supposed I could either use an IF-THEN block for every output, but I'd like to avoid that if I could. Any ideas?