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

 

C++

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Symbols index

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Input/output library

I/O manipulators

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

basic_spanbuf (C++23)

strstreambuf (deprecated in C++98)

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basic_osyncstream (C++20)

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std::basic_ios

Member functions

basic_ios::basic_ios

basic_ios::~basic_ios

State functions

basic_ios::good

basic_ios::eof

basic_ios::fail

basic_ios::bad

basic_ios::operator!

basic_ios::operator bool

basic_ios::rdstate

basic_ios::setstate

basic_ios::clear

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basic_ios::copyfmt

basic_ios::fill

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basic_ios::exceptions

basic_ios::imbue

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basic_ios::widen

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basic_ios::init

basic_ios::move (C++11)

basic_ios::swap (C++11)

basic_ios::set_rdbuf (C++11)

 

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 | 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

See also

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