C pointers and the physical address

Question

I\'m just starting C. I have read about pointers in various books/tutorials and I understand the basics. But one thing I haven\'t seen explained is what are the numbers.

Answer 1

A lot of people told you, that the numeric value of a pointer will designate its address. This is one way how implementations can do it, but it is very important, what the C standard has to say about pointers:

• The nil pointer has always numeric value 0 when operated on in the C programming language. However the actual memory containing the pointer may have any value, as long as this special, architecture dependent value is consistently treated nil, and the implementation takes care that this value is seen as 0 by C source code. This is important to know, since 0 pointers may appear as a different value on certain architectures when inspected with a low level memory debugger.
• There's no requirement whatsoever that the values of the pointer are in any way related to actual addresses. They may be as well abstract identifiers, resolved by a LUT or similar.
• If a pointer addresses an array, the rules of pointer arithmetic must hold, i.e. int array[128]; int a, b; a = (int)&array[120]; b = (int)&array[100]; a - b == 20 ; array + (a-b) == &array[20]; &array[120] == (int*)a
• Pointer arithmetic between pointers to different objects is undefined and causes undefined behaviour.
• The mapping pointer to integer must be reversible, i.e. if a number corresponds to a valid pointer, the conversion to this pointer must be valid. However (pointer) arithmetic on the numerical representation of pointers to different objects is undefined.