extraction-operator

问题 If calling something like input_stream >> i; where i is of arithmetic type, throws exception or sets badbit etc., is it guaranteed that i has not changed? 回答1: Before C++11, the value was left as it was, [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) But after C++11, no. It is set to 0 if extraction fails (same reference): If extraction fails, zero is written to value and failbit is set. If

问题 Some of the standard iomanip functions take take a parameter. I'd like to know how this is accomplished, for instance, can I do something similar with a function? That's really the solution that I needed for this answer, but I couldn't figure out how to do this. When I looked up the definition for setw function for example in http://en.cppreference.com it lists the return type as "unspecified", and it also only lists one argument, rather than also taking a stream& parameter. How does this

问题 Given a string that should represent a number, I'd like to put it into a conversion function which would provide notification if the whole string did not convert. For input: "12" : istringstream::operator>> outputs 12 atoi outputs 12 stoi outputs 12 For input "1X" I'd like a failure response but I get: istringstream::operator>> outputs 1 atoi outputs 1 stoi outputs 1 For input "X2" : istringstream::operator>> outputs 0 and sets an error flag atoi outputs 0 stoi throws an error [Live Example]