问题描述
这是C ++入门第五版问题3.26中的问题，我不知道它们之间的区别吗?可能是第二个可以避免溢出.
It is a problem from C++ primer fifth edition problem 3.26, I don't know the difference between them ?May be the second one can avoid overflow.
推荐答案
完全正确.不能保证beg+end是可表示的；但是在第二种情况下，中间值以及预期结果均不大于end，因此没有溢出的危险.
Exactly. There's no guarantee that beg+end is representable; but in the second case the intermediate values, as well as the expected result, are no larger than end, so there is no danger of overflow.
第二种形式也可以用于仿射类型，例如指针和其他随机访问迭代器，可以将它们减去以得出距离，但不能加在一起.
The second form can also be used for affine types like pointers and other random-access iterators, which can be subtracted to give a distance, but not added together.
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