nullptr

The null pointer is a pointer guaranteed not to point to valid data. Traditionally, C++ has represented this pointer in source code with 0, although the internal representation could be different. This raises some problems because it makes 0 both a pointer constant and an integer constant. As discussed in Chapter 12, “Classes and Dynamic Memory Allocation,” C++11 introduces the keyword nullptr to represent the null pointer; it is a pointer type and not convertible to an integer type. For backward compatibility, C++ still allows the use of 0, and the expression nullptr == 0 evaluates as true, but using nullptr instead of 0 provides better type safety. For example, the value 0 could be passed to a function accepting an int argument, but the compiler will identify an attempt to pass nullptr to such a function as an error. So, for clarity and added safety, use nullptr if your compiler accepts it.