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c++parsingistream

istream extraction operator: how to detect parse failure?

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

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

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).

Solution

  • 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 ;

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