ptrdiff_t
The prtdiff_t type is defined in stddef.h. This type specifies the signed integer result of subtracting two pointers. It is defined as:
typedef int ptrdiff_t;
and is used as shown in the following example:
#include <stddef.h>
void pfunc (void *p1, void *p2) {
ptrdiff_t pdiff;
pdiff = p1 -p2;
}