Not sure if K & R is correct - pointer arithmetic | Release procedure

Quote:

The if (allocbuf + ALLOCSIZE - allocp> = n) {test checks if there is enough space to satisfy a request for n characters. If there is, then the new allocp value will be no more than one outside of the allocbuf.

Code to which it relates:

#define ALLOCSIZE 10000 /* size of available space */
static char allocbuf[ALLOCSIZE]; /* storage for alloc */
static char *allocp = allocbuf; /* next free position */

char *alloc(int n)
/* return pointer to n characters */
{
    if (allocbuf + ALLOCSIZE - allocp >= n) { /* it fits */
        allocp += n;
        return allocp - n; /* old p */
    } else
/* not enough room */
        return 0;
}
void afree(char *p) /* free storage pointed to by p */
{
    if (p >= allocbuf && p < allocbuf + ALLOCSIZE)
        allocp = p;
}

So how can this be behind the last position in allocbuf? Which, in my opinion, is allocbuf [9999]

Anything besides this, for example. allocbuf [10000] is incorrect and is a memory leak, right?

- afree , . , , " " ? .