g++ does not show a 'unused' warning

Question

I have a little piece of code in C++:

#include 
#include 
#include 

using namespace std;

int main() {

    in         


        

Answer 1

istream_iterator has a constructor, so the declaration of EOS isn't really a no-op like the declarations of i and x are.

Often you want to declare a class-type object and then not do anything with it. For example, consider std::lock_guard in C++0x (boost::scoped_lock in Boost) or any other kind of scope guard class. You don't usually want to do anything with that kind of object, you just want to create the object so that its destructor get run at the end of the block to perform whatever cleanup needs to be performed.