c++ - 是否保证标准提取运算符>>在失败的情况下不会更改参数？

Question

如果调用input_stream >> i;，其中i是算术类型，抛出异常或设置badbit等，是否保证i没有改变？

Answer 1

在 C++11 之前，该值保持原样，[reference] :

If extraction fails (e.g. if a letter was entered where a digit is expected), value is left unmodified and failbit is set. (until C++11)

但在 C++11 之后，没有。它设置为 0如果提取失败(相同的引用):

If extraction fails, zero is written to value and failbit is set. If extraction results in the value too large or too small to fit in value, std::numeric_limits<T>::max() or std::numeric_limits<T>::min() is written and failbit flag is set. (since C++11)