XCode 4 only displaying cout statements with endl

问题

I have a really weird issue with my cout statements. I've only tried this out with XCode 4. For instance, if I write,

cout << "this works" << endl;
cout << "this doesnt";
cout << memorySizeLimit << " blocks of memory available." << endl;

I see all three output statements in my debugger console. However, if I change the order to,

cout << memorySizeLimit << " blocks of memory available." << endl;
cout << "this works" << endl;
cout << "this doesn't";

I only see the first two couts. Even stranger, if I change the code to,

cout << memorySizeLimit << " blocks of memory available." << endl;
cout << "this works" << endl;
cout << "this doesn't" << endl;

I see all three statements.

Why would I not see that "this doesn't" cout statement when I change its position?

回答1:

std::cout is an stream and normally it is buffered for performance. If you print endl the stream gets flushed (cout << endl is the same as cout << "\n" << flush.

You may flush the stream manually by cout << flush (or cout.flush()).

So that should print:

cout << "this doesn't" << flush;

来源：https://stackoverflow.com/questions/5453071/xcode-4-only-displaying-cout-statements-with-endl