NAME¶

std::basic_ios::clear - std::basic_ios::clear

Synopsis¶

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¶

new error state flags setting. It can be a combination of the following
constants:

state - 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
an excption would be thrown if the current
LWG 412 C++98 error state checks the new
includes a bit that is also included in the error state instead
exceptions() mask

See also¶

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