what does this declaration mean? exception() throw()

Question

std::exception class is defined as follows

exception() throw() { }
virtual ~exception() throw();
virtual const char* what() const throw();

Answer 1

It's an "exception specification". throw() means "this function will not throw any exceptions". You can also specify exceptions, so throw(foo) would say this function may throw exceptions of type foo.

The usefulness of this feature has been debated quite a bit in the C++ community - the general evaluation seems to be that it is not particularly useful. For more details take a look at this Herb Sutter article.