is std::cout thread safe?

[xyzt]

std::cout object is defined as: [Stroustrup says in his book]

namespace std {
class ostream {
//...
ostream& operator<<(const char*);
};
extern ostream cout;

So, as I see in this code, there's actually 1 cout object for each process. If a multi-threaded application tries to use std::cout object, will it be safe?

[Athar]

Yes, however if you run this in two different threads:

cout << "Hello World!" << endl;

then the other thread might get to print something in-between "Hello World" and endl, so you can end up with lines like "Hello World!Hello World!".
So in most cases you still have to synchronize cout access.