c - 指针有问题吗？

Question

我在理解 *binsearch 函数中某些代码行的机制时遇到了问题。特别是，low 和 high 是两个指针，分别初始化为 &tab[0] 和 &tab[n]。在下一行中，我看到 low<high我认为它无效，因为无法比较两个指针的两个地址。下一行也有同样的问题。我不知道我是否正确，我需要大家的一些想法。

#include <stdio.h>
#include <ctype.h>
#include <string.h>
#define MAXWORD 100
int getword(char *, int);
struct key *binsearch(char *, struct key *, int);
/* count C keywords; pointer version */
main()
{
    char word[MAXWORD];
    struct key *p;
    while (getword(word, MAXWORD) != EOF)
        if (isalpha(word[0]))
            if ((p=binsearch(word, keytab, NKEYS)) != NULL)
                p->count++;
    for (p = keytab; p < keytab + NKEYS; p++)
        if (p->count > 0)
            printf("%4d %s\n", p->count, p->word);
    return 0;
}
/* binsearch: find word in tab[0]...tab[n-1] */
struct key *binsearch(char *word, struck key *tab, int n)
{
    int cond;
    struct key *low = &tab[0];
    struct key *high = &tab[n];
    struct key *mid;
    while (low < high) {
        mid = low + (high-low) / 2;
        if ((cond = strcmp(word, mid->word)) < 0)
            high = mid;
        else if (cond > 0)
            low = mid + 1;
        else
            return mid;
    }
    return NULL;
}

Answer 1

如果两个指针属于同一数组，则可以比较它们。

特别是这些是您可以使用或不使用指针执行的操作:

• Pointer comparison is Valid only if the two pointers are Pointing to same array.

• All Relational Operators can be used for comparing pointers of same type.

• All Equality and Inequality Operators can be used with all Pointer types.

• Pointers cannot be Divided or Multiplied.

所以 low < high在这种情况下是允许的并且运行良好。