What are the rules for subtracting two pointers in C?

What are the rules for subtracting two pointers in C?

When two pointers are subtracted, both must point to elements of the same array object or just one past the last element of the array object (C Standard, 6.5. 6 [ISO/IEC 9899:2011]); the result is the difference of the subscripts of the two array elements. Otherwise, the operation is undefined behavior.

Can we do subtraction of two pointers?

The subtraction of two pointers is possible only when they have the same data type. The result is generated by calculating the difference between the addresses of the two pointers and calculating how many bits of data it is according to the pointer data type.

Can you subtract pointers from each other in C?

Two pointers can also be subtracted from each other if the following conditions are satisfied: Both pointers will point to elements of same array; or one past the last element of same array. The result of the subtraction must be representable in ptrdiff_t data type, which is defined in stddef.

How null pointer is defined?

A null pointer is a pointer which points nothing. Some uses of the null pointer are: a) To initialize a pointer variable when that pointer variable isn’t assigned any valid memory address yet. b) To pass a null pointer to a function argument when we don’t want to pass any valid memory address.

What happens when you subtract pointers?

Pointer Subtraction The result is the distance (in array elements) between the two elements. This can result in negative values if p2 has a smaller address than p1. p2 and p1 need not point to valid elements in an array.

Can two pointers be compared?

Pointers of the same type (after pointer conversions) can be compared for equality. Two pointers of the same type compare equal if and only if they are both null, both point to the same function, or both represent the same address (3.9. 2).

IS null always defined as 0 zero )?

The null pointer constant is always 0. The NULL macro may be defined by the implementation as a naked 0 , or a cast expression like (void *) 0 , or some other zero-valued integer expression (hence the “implementation defined” language in the standard). The null pointer value may be something other than 0.

What is null defined as in C?

In computer programming, null is both a value and a pointer. Null is a built-in constant that has a value of zero. It is the same as the character 0 used to terminate strings in C. Null can also be the value of a pointer, which is the same as zero unless the CPU supports a special bit pattern for a null pointer.

What is value of null in C?

The value of NULL macro is 0. It is defined in C header files as below. #define NULL (void *) 0; NULL is used for pointers only as it is defined as (void *) 0. If NULL is assigned to a pointer, then pointer is pointing to nothing.

WHAT IS null pointer and void pointer?

A null pointer is basically a null value assigned to a pointer of any data type whereas a void pointer is a data type which remains void as long as an address of a data type is not assigned to it. Null pointer does not contain a reference of any variable/value.

Is it possible to subtract a pointer from an object?

The standard acknowledges that possibility, though it explicitly defines the behavior only for an equality comparison between a pointer past the end of one object and a pointer to an adjacent object. See N15706.5.9 paragraphs 6-7. For subtraction, you should just assume the behavior is undefined.

Is it possible to increment a null pointer?

Apart from the possibility that incrementing a null pointer might just crash on some hardware, what about this: Since incrementing a null pointer is undefined behavour, the compiler checks whether a pointer is null and only increments the pointer if it isn’t a null pointer, so p + 1 is again a null pointer.

Why does my program crash when I call f(0) instead of 0?

The compiler is therefore allowed to remove the x == 0 check in the return statement and just return 1000000 / x. Which means your program crashes when you call f (0) instead of returning 0. Another assumption made was that if you increment a null pointer and then decrement it again, the result is again a null pointer. Wrong again.

How to find the distance between two pointers in an array?

The subtraction of two pointers in array will give the distance between the two elements. Let the address of first element i.e., is 1000 then address of second element a+1 will be 1004. Hence p1 = 1000 and p2 =1004. Thanks for contributing an answer to Stack Overflow!