<P> In computing, a null pointer has a value reserved for indicating that the pointer does not refer to a valid object . Programs routinely use null pointers to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to nullable types and to the Nothing value in an option type . </P> <P> A null pointer should not be confused with an uninitialized pointer: A null pointer is guaranteed to compare unequal to any pointer that points to a valid object . However, depending on the language and implementation, an uninitialized pointer may not have any such guarantee . It might compare equal to other, valid pointers; or it might compare equal to null pointers . It might do both at different times . </P> <P> In C, two null pointers of any type are guaranteed to compare equal . The preprocessor macro NULL is defined as an implementation - defined null pointer constant, which in C99 can be portably expressed as the integer value 0 converted implicitly or explicitly to the type void * (pointer to void). The C standard does not say that the null pointer is the same as the pointer to memory address 0, though that may be the case in practice . Dereferencing a null pointer is undefined behavior in C, and a conforming implementation is allowed to assume that any pointer that is dereferenced is not null . </P> <P> In practice, dereferencing a null pointer may result in an attempted read or write from memory that is not mapped, triggering a segmentation fault or memory access violation . This may manifest itself as a program crash, or be transformed into a software exception that can be caught by program code . There are, however, certain circumstances where this is not the case . For example, in x86 real mode, the address 0000: 0000 is readable and also usually writable, and dereferencing a pointer to that address is a perfectly valid but typically unwanted action that may lead to undefined but non-crashing behavior in the application . There are occasions when dereferencing the pointer to address zero is intentional and well - defined; for example, BIOS code written in C for 16 - bit real - mode x86 devices may write the IDT at physical address 0 of the machine by dereferencing a null pointer for writing . It is also possible for the compiler to optimize away the null pointer dereference, avoiding a segmentation fault but causing other undesired behavior . </P>

What is the value of null in c
find me the text answering this question