我正在阅读K& R中关于阵列算术的部分,并且遇到了一些奇怪的事情.我发布了整段内容,但我主要关注的是大胆的部分.
If p and q point to members of the same array,then relations like ==,@H_403_4@ !=,<,>=,etc.,work properly. For example,p < q is true if p points@H_403_4@ to an earlier member of the array than q does. Any pointer can be@H_403_4@ meaningfully compared for equality or inequality with zero. But the@H_403_4@ behavior is undefined for arithmetic or comparisons with pointers that@H_403_4@ do not point to members of the same array. (There is one exception:@H_403_4@ the address of the first element past the end of an array can be used@H_403_4@ in pointer arithmetic.)
这个例外的原因是什么？在定义大小时,是否将额外的内存分配给任何数组的末尾？如果是这样,为了什么目的？是用空字符结束数组吗？
解决方法
原因是你可以在循环中增加指针,如下所示：
char a[42],*p;
for (p = a; p < &a[sizeof a]; p++) // or p != &a[sizeof a]
{
/* ... */
}
如果没有额外的规则,这将是未定义的行为,因为指针将无效.
