NULLED

 NULL in the programming languages C and C + + - macros declared in the header file stddef.h (and other header files). The value of this macro is a constant depending on the implementation of the zero index (eng. null pointer constant). Constant zero pointer - this is an integer constant expression with value 0, or (in C) is the same expression, but reduced to the type void *. Constant zero pointer given to any type of indicator is a zero pointer. Guaranteed that the pointer is not equal to zero the pointer to any object (in the broadest sense, any data) or function. Guaranteed that any two null pointer equal. Razymenovyvanie zero pointer is a transaction with an uncertain behavior. 

In other words, the implementation provides a special value - a constant of zero index, which you can assign a pointer and a pointer in comparison will not be equal to any «correct» the signs. That is, it may be assumed that the zero does not contain a valid pointer address in memory.

NULLED