矢量走出边界，而不给出错误 [英] Vector going out of bounds without giving error

问题描述

我有一个 std :: vector 。我检查它的大小是6，但是当我尝试访问 vec [6] 以检查它是否会给错误，我得到没有错误，但有一些数字。不应该出现错误吗？

I have a std::vector. I check its size which is 6 but when I try to access vec[6] to check whether it will give error, I get no error but some number instead. Should not it give an error?

编辑：例如：

struct Element
{
    std::vector<double> face;
};

int main()
{
    Element elm;

    .... // insert 6 elements into elm.face

    std::cout << elm.face.size() << std::endl; // answer is 6
    std::cout << elm.face[6] << std::endl; // answer is some number
}

推荐答案

STL向量在调用 .at（）成员函数时执行边界检查，但不对 [] 运算符执行任何检查。

STL vectors perform bounds checking when the .at() member function is called, but do not perform any checks on the [] operator.

当超出范围时， [] 运算符产生未定义的结果。

When out of bounds, the [] operator produces undefined results.

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