std::basic_...am::is_open(3)

✨ NAME ✨

std::basic_ifstream::is_open — bestie, it's literally std::basic_ifstream::is_open 💅

(this is a page from the C++ Standard Library manual, btw — keeping you informed 🫶)

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🌸 SYNOPSIS 🌸

okay so here's the whole vibe, no cap:

bool is_open() const;

What it does? Checks if the file stream has an associated file. That's it. That's the function. 🎀

Under the hood it's effectively calling rdbuf()->is_open(), so like, it's not doing anything magical — it's just asking its buddy rdbuf() to do the actual checking. iykyk ✨

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🦋 PARAMETERS 🦋

• (none) — bestie takes zero arguments, she needs NOTHING from you 💀

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⭐ RETURN VALUE ⭐

• true — if the file stream has an associated file 🎉
• false — otherwise 😭

that's the whole thing. very demure. very mindful. 🌈

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🔥 EXAMPLE 🔥

// Run this code

#include <fstream>
#include <iostream>
#include <string>

// this file is called main.cpp

bool file_exists(const std::string& str)
{
    std::ifstream fs(str);
    return fs.is_open();
}

int main()
{
    std::boolalpha(std::cout);
    std::cout << file_exists("main.cpp")  << '\n'
              << file_exists("strange_file") << '\n';
}

okay so notice std::boolalpha(std::cout) — that's the main character move that makes it print true/false instead of 1/0. obsessed. 👑

🌸 Possible output 🌸

true
false

like, main.cpp exists (obviously, it's right there), and strange_file... does not. the audacity honestly 🙈

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💜 DEFECT REPORTS 💜

so there were these behavior-changing defect reports that got applied retroactively to previously published C++ standards — which is lowkey wild when you think about it, they went back and fixed the past 💀

Here's the tea:

• DR: LWG 365
• Applied to: C++98
• Behavior as published: is_open was not declared with const qualifier
• Correct behavior: declared with const qualifier

so yeah, it got that const glow-up and honestly she deserved it 🎀✨

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🧚 SEE ALSO 🧚

• open — opens a file and associates it with the stream (public member function) 🦋
• close — closes the associated file (public member function) 💅

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and that's the page bestie!! go check your streams, stay hydrated, and remember: if is_open() returns false, it's not you, it's the file path 😭💖

💖 courtesy of http://cppreference.com — version 2024.06.10 — slay safe out there 🎀✨