Subtracting two pointers giving unexpected result

Question

#include 

int main() {
    int *p = 100;
    int *q = 92;
    printf(\"%d\\n\", p - q);  //prints 2
}

Shouldn\'t the output of above pr

Answer 1

Your code is undefined behavior.

You cannot simply subtract two "arbitrary" pointers. Quoting C11, chapter §6.5.6/P9

When two pointers are subtracted, both shall point to elements of the same array object, or one past the last element of the array object; the result is the difference of the subscripts of the two array elements. The size of the result is implementation-defined, and its type (a signed integer type) is ptrdiff_t defined in the header. [....]

Also, as mentioned above, if you correctly subtract two pointers, the result would be of type ptrdiff_t and you should use %td to print the result.

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That being said, the initialization

 int *p = 100;

looks quite wrong itself !! To clarify, it does not store a value of 100 to the memory location pointed by (question: where does it point to?) p. It attempts to sets the pointer variable itself with an integer value of 100 which seems to be a constraint violation in itself.