std::basic_istream<CharT,Traits>::ignore

basic_istream& ignore( std::streamsize count = 1, int_type delim = Traits::eof() );

Extracts and discards characters from the input stream until and including delim.

ignore behaves as an UnformattedInputFunction. After constructing and checking the sentry object, it extracts characters from the stream and discards them until any of the following conditions occurs:

• count characters were extracted. This test is disabled in the special case when count equals std::numeric_limits<std::streamsize>::max()
• end of file conditions occurs in the input sequence, in which case the function calls setstate(eofbit)
• the next available character c in the input sequence is delim, as determined by Traits::eq_int_type(Traits::to_int_type(c), delim). The delimiter character is extracted and discarded. This test is disabled if delim is Traits::eof().

Parameters

Return value

*this.

Exceptions

If an internal operation throws an exception, it is caught and badbit is set. If exceptions() is set for badbit, the exception is rethrown.

Example

#include <iostream>
#include <sstream>
#include <limits>
 
constexpr auto max_size = std::numeric_limits<std::streamsize>::max();
 
int main()
{
    std::istringstream input("1\n"
                             "some non-numeric input\n"
                             "2\n");
    for (;;)
    {
        int n;
        input >> n;
 
        if (input.eof() || input.bad())
            break;
        else if (input.fail())
        {
            input.clear(); // unset failbit
            input.ignore(max_size, '\n'); // skip bad input
        }
        else
            std::cout << n << '\n';
    }
}

1
2

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also