《C专家编程》里面提到了"The One 'l' nul and the Two 'l' null",网上查了一下,得到了一个更详细的区分。
NULL is a macro defined in several standard headers, 0 is an integer constant, '\0' is a character constant, and nul is the name of the character constant. All of these are not interchangeable:
NULL is to be used for pointers only since it may be defined as ((void *)0), this would cause problems with anything but pointers.
0 can be used anywhere, it is the generic symbol for each type's zero value and the compiler will sort things out.
'\0' should be used only in a character context.
nul is not defined in C or C++, it shouldn't be used unless you define it yourself in a suitable manner, like: