tips for subscript operator

最新推荐文章于 2023-09-17 17:03:29 发布

Achilles_K

最新推荐文章于 2023-09-17 17:03:29 发布

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分类专栏： C++ 文章标签： subscript vector array string

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本文通过《C++ Primer》中的一段话强调了C++内置数组与标准库类型如vector和string在使用下标操作符时的区别。对于内置数组而言，下标可以接受负数，而vector和string则强制要求下标为非负数。

Quote from the << C++ prime>>:

"""

int *p = &ia[2]; // ia[] is a int-type array, it contains 5 elements.

int j = p[1];

int k = p[-2];

This last example points out an imiportant difference between arrays and library types such as vector and string that have subscript operators. The library types force the index used with a subscript to be an unsigned value. The built-in subscript operator does not. The index used with the built-in subscript operator can be a negative value. Of course, the resulting address must point to an element in (or one past the end of ) the array to which the original pointer points.

"""

The paragraph stress the difference of subscript-operator for different types.. the index used with the built-in subscript operator can't be a negative value for vector and string.

Warning:

Unlike subscripts for vector and string, the index of the built-in subscript operator is not an unsigned type.