std::basic_ios::eof(3)

💖 std::basic_ios::eof(3) 💖

okay bestie, this is the C++ Standard Libary manual page for std::basic_ios::eof (yep, that's the spelling in the header 😭), and it's literally all about checking whether your stream hit end-of-file.

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✨ NAME ✨

std::basic_ios::eof - std::basic_ios::eof

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🌸 Synopsis 🌸

bool eof() const;

Returns true if the associated stream has reached end-of-file. Specifically, returns true if eofbit is set in rdstate().

See ios_base::iostate for the list of conditions that set eofbit.

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🎀 Parameters 🎀

(none) — literally not a single parameter, she takes no args and has no drama.

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💖 Return value 💖

true if an end-of-file has occurred, false otherwise.

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🧚 Notes 🧚

okay so the important thing: this function only reports the stream state as set by the most recent I/O operation; it does not examine the associated data source.

For example, if the most recent I/O was a get() which returned the last byte of a file, eof() returns false. The next get() fails to read anything and sets the eofbit. Only then does eof() return true.

In typical usage, input stream processing stops on any error. eof() and fail() can then be used to distinguish between different error conditions.

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🔥 Example 🔥

// Run this code

#include <cstdlib>
#include <fstream>
#include <iostream>

int main()
{
    std::ifstream file("test.txt");
    if (!file) // operator! is used here
    {
        std::cout << "File opening failed\n";
        return EXIT_FAILURE;
    }

    // typical C++ I/O loop uses the return value of the I/O function
    // as the loop controlling condition, operator bool() is used here
    for (int n; file >> n;)
       std::cout << n << ' ';
    std::cout << '\n';

    if (file.bad())
        std::cout << "I/O error while reading\n";
    else if (file.eof())
        std::cout << "End of file reached successfully\n";
    else if (file.fail())
        std::cout << "Non-integer data encountered\n";
}

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👑 See also 👑

The following shows the value of basic_ios accessors (good(), fail(), etc.) for all possible combinations of ios_base::iostate flags:

Columns, in order: ios_base::iostate flags eofbit, failbit, badbit; then basic_ios accessors good(), fail(), bad(), eof(), operator bool, operator!.

• eofbit false, failbit false, badbit false → good() true, fail() false, bad() false, eof() false, operator bool true, operator! false.
• eofbit false, failbit false, badbit true → good() false, fail() true, bad() true, eof() false, operator bool false, operator! true.
• eofbit false, failbit true, badbit false → good() false, fail() true, bad() false, eof() false, operator bool false, operator! true.
• eofbit false, failbit true, badbit true → good() false, fail() true, bad() true, eof() false, operator bool false, operator! true.
• eofbit true, failbit false, badbit false → good() false, fail() false, bad() false, eof() true, operator bool true, operator! false.
• eofbit true, failbit false, badbit true → good() false, fail() true, bad() true, eof() true, operator bool false, operator! true.
• eofbit true, failbit true, badbit false → good() false, fail() true, bad() false, eof() true, operator bool false, operator! true.
• eofbit true, failbit true, badbit true → good() false, fail() true, bad() true, eof() true, operator bool false, operator! true.
• feof checks for the end-of-file — (function)

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mwah 💋 source/version/date vibes: http://cppreference.com, 2024.06.10, and page std::basic_ios::eof(3). byeee, go read some streams 🫶