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//using namespace std; using std::ifstream; using std::ofstream; using std::cout; class Dog { friend ostream& operator<< (ostream&, const Dog&); public: char* name; char* breed; char* gender; Dog(); ~Dog(); }; im trying to overload the << operator. I'm also trying to practice good coding. But my code wont compile unless i uncomment the using namespace std. i keep getting this error and i dont know. im using g++ compiler. Dog.h:20: error: ISO C++ forbids declaration of ‘ostream’ with no type Dog.h:20: error: ‘ostream’ is neither function nor member function; cannot be declared friend. if i add

I've been told by others that writing using namespace std; in code is wrong, and that I should use std::cout and std::cin directly instead. Why is using namespace std; considered a bad practice? Is it inefficient or does it risk declaring ambiguous variables (variables that share the same name as a function in std namespace)? Does it impact performance? Greg Hewgill This is not related to performance at all. But consider this: you are using two libraries called Foo and Bar: using namespace foo; using namespace bar; Everything works fine, and you can call Blah() from Foo and Quux() from Bar

From std::add_pointer Possible implementation namespace detail { template <class T> struct type_identity { using type = T; }; // or use std::type_identity (since C++20) template <class T> auto try_add_pointer(int) -> type_identity<typename std::remove_reference<T>::type*>; template <class T> auto try_add_pointer(...) -> type_identity<T>; } // namespace detail template <class T> struct add_pointer : decltype(detail::try_add_pointer<T>(0)) {}; The description for the above (possible) implementation reads: If T is a reference type, then provides the member typedef type which is a pointer to the

I recently passed a null pointer to a std::string constructor and got undefined behavior. I'm certain this is something that thousands or tens of thousands of programmers have done before me, and this same bug has no doubt crashed untold numbers of programs. It comes up a lot when converting from code using char* to code using std::string , and it's the kind of thing that is not catchable at compile time and can easily be missed in run time unit tests. What I'm confused about is the reason for specifying std::string this way. Why not just define std::string(NULL)=="" ? The efficiency loss