std::basic_ios<CharT,Traits>::clear
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void clear( std::ios_base::iostate state = std::ios_base::goodbit );
Sets the stream error state flags by assigning them the value of state. By default, assigns std::ios_base::goodbit which has the effect of clearing all error state flags.
If rdbuf() is a null pointer (i.e. there is no associated stream buffer), then state | std::ios_base::badbit is assigned.
[edit] Parameters
state
-
new error state flags setting. It can be a combination of the following constants:
Constant
Explanation
goodbit
no error
badbit
irrecoverable stream error
failbit
input/output operation failed (formatting or extraction error)
eofbit
associated input sequence has reached end-of-file
[edit] Return value
(none)
[edit] Exceptions
If the new error state includes a bit that is also included in the exceptions() mask, throws an exception of type failure .
[edit] Example
clear() without arguments can be used to unset the failbit after unexpected input; for std::cin.putback(c) see ungetc.
Run this code
#include <iostream> #include <string> int main() { for (char c : {'\n', '4', '1', '.', '3', '\n', 'Z', 'Y', 'X'}) std::cin.putback(c); // emulate user's input (not portable: see ungetc Notes) double n; while (std::cout << "Please, enter a number: " && !(std::cin >> n)) { std::cin.clear(); std::string line; std::getline (std::cin, line); std::cout << line << "\nI am sorry, but '" << line << "' is not a number\n"; } std::cout << n << "\nThank you for entering the number " << n << '\n'; }
Output:
Please, enter a number: XYZ I am sorry, but 'XYZ' is not a number Please, enter a number: 3.14 Thank you for entering the number 3.14
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 412 | C++98 | an excption would be thrown if the current error state includes a bit that is also included in the exceptions() mask |
checks the new error state instead |