# std::basic_ios<CharT,Traits>::clear

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< cpp‎ | io‎ | basic ios

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)

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