namespace C++ {}

Why nullptr ? what is nullptr ? But we already have NULL why nullptr ? Well the problem is how to distinguish between NULL and 0? we have #define NULL 0. The NULL pointer and an integer 0 cannot be distinguished well for overload resolution. For example, given two overloaded functions The call f(0) unambiguously resolves to f(int). There is no way to write a call to f(char*) with a null pointer value without writing an explicit cast (i.e., f((char*)0)) or using a named variable. Naming NULL Further, programmers have often requested that the null pointer constant have a name (rather than just 0). This is one reason why the macro NULL exists, although that macro is insufficient. (If the null pointer constant had a type-safe name, this would also solve the previous problem as it could be distinguished from the integer 0 for overload resolution and some error detection.) To avoid these problems, 0 must mean only one thing (an integer value), and we need to have a different name t