istream提取运算符：如何检测解析失败？ [英] istream extraction operator: how to detect parse failure?

问题描述

如何检测istream提取是否失败？

How can I detect whether the istream extraction failed like this?

string s("x");
stringstream ss(s);
int i;
ss >> std::ios::hex >> i;

编辑 - 虽然问题标题涵盖了这一点，我忘了在身体提到：以检测故障是由于格式不良（即解析）还是由于任何其他IO相关的问题，以提供适当的反馈（一个malformed_exception（x）或其他）。

EDIT -- Though the question title covers this, I forgot to mention in the body: I really want to detect whether the failure is due to bad formatting, i.e. parsing, or due to any other IO-related issue, in order to provide proper feedback (an malformed_exception("x") or whatever).

推荐答案

首先：感谢有用的答案。但是，经过一番调查（cfr。 cppreference ）和验证后，似乎检查解析失败的唯一方法是检查 ios :: failbit 标志，如

First off: thanks for the useful answers. However, after some investigation (cfr. cppreference) and verification, it seems that the one way to check for parse-failure only is by checking for the ios::failbit flag, as in

const bool parsing_failed = (ss >> ios::hex >> i).rdstate() & ios::failbit ;

虽然建议的 istream :: operator！和 istream :: operator bool mingle failbit （cfr 这里和 there on cplusplusreference）。

While both the suggested istream::operator! and istream::operator bool mingle failbit and badbit (cfr here and there on cplusplusreference).

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