std::basic_istream::ignore(3)

💅 std::basic_istream::ignore 💅

okay bestie, welcome to the std::basic_istream::ignore(3) page from the C++ Standard Libary manual 💖 this one is literally about yeeting characters out of an input stream, and ngl it's kind of iconic.

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🌸 NAME 🌸

std::basic_istream::ignore — yep, it's std::basic_istream::ignore again, main character energy 💅

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📜 Synopsis 📜

Here's the signature, bestie — copy it exactly, no cap:

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

So what does it do? It extracts and discards characters from the input stream until and including delim. Bye-bye, unwanted input 🫶

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

• count characters were extracted. This test is disabled in the special case when count equals std::numeric_limits<std::streamsize>::max().
• an end-of-file condition 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().

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🎀 Parameters 🎀

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

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✨ Return value ✨

• *this

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🔥 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.

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🦋 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

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💀 Defect reports 💀

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

• DR LWG 172 — applied to C++98: the type of count was misspecified as int; the corrected behavior is std::streamsize.

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👑 See also 👑

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

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mwah 💋 this page came from http://cppreference.com, dated 2024.06.10, for std::basic_istream::ignore(3) — k bye bestie, go ignore some bad input 🫶✨