c++ - 当字符串下标超出范围时，不抛出异常

Question

此代码不打印任何内容，但也不会产生错误。为什么？

string s = "test";
cout << s[5];

Answer 1

std::string 的operator[] 是documented to not do any bounds checking :

Returns a reference to the character at specified location pos. No bounds checking is performed.

要使用边界检查从字符串中读取，请使用 at() :

Returns a reference to the character at specified location pos. Bounds checking is performed, exception of type std::out_of_range will be thrown on invalid access.