I am trying to understand this program from my class I under

  I am trying to understand this program from my class.  I understnad the basic form of the throw catch excption, but I don\'t understand what the cerr function does.  It looks like it\'s for an output error msg of sorts?   Anyways, when I run this program, it doesn\'t output the error msg even though p.fly is called. can someone explain this?    Thanks in advance.     // #include<iostream> #include<string> using namespace std;  class BirdException {    public:   BirdException(const string s) : msg(s) {}  // Does this imply that it is inhearting the msg function for this class?     string msg; };  class Bird {   public:     virtual void fly(void) = 0; };  class Penguin : public Bird {   public:     virtual void fly(void)     {       throw BirdException(\"oops, penguins can\'t fly\");     } };  int main() {   Penguin p;    try   {     p.fly();   }   catch ( BirdException& be )   {     cerr << \"Exception caught: \" << be.msg << endl;   } }