 Dereferencing a null pointer value is undefined, often resulting in a segmentation fault.Null pointer values are useful for indicating special cases such as no "next" pointer in the final node of a linked list, or as an error indication from functions returning pointers.In appropriate contexts in source code, such as for assigning to a pointer variable, a "null pointer constant" can be written as codice_79, with or without explicit casting to a pointer type, or as the codice_217 macro defined by several standard headers.