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.

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

Return value

(none)

Exceptions

If the new error state includes a bit that is also included in the exceptions() mask, throws an exception of type failure.

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

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

See also

setstate	sets state flags (public member function)
rdstate	returns state flags (public member function)