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

 

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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

count	-	number of characters to extract
delim	-	delimiting character to stop the extraction at. It is also extracted

Return value

*this

Exceptions

failure if an error occurred (the error state flag is not goodbit) and exceptions() is set to throw for that state.

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

The following example uses ignore to skip over non-numeric input:

Run this code

#include <iostream>
#include <limits>
#include <sstream>
 
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';
    }
}

Output:

1
2

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 172	C++98	the type of count was misspecified as int	corrected to std::streamsize

See also

get	extracts characters (public member function)
getline	extracts characters until the given character is found (public member function)