fclose(3)

✨ fclose(3) — Library Functions Manual ✨

okay bestie, gather round, because today we're closing a stream and it's honestly iconic 💖

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💫 NAME 💫

fclose — close a stream

📚 LIBRARY 📚

Standard C library (libc, -lc) — she's literally built in, no extra linking required, we love a low-maintenance queen 👑

🎀 SYNOPSIS 🎀

#include <stdio.h>

int fclose(FILE *stream);

🦋 DESCRIPTION 🦋

So the way this works is: fclose() flushes the stream that stream points to — like, it writes out any buffered output data that's still chilling in the buffer, using fflush(3) for the actual flushing — and then it closes the underlying file descriptor.

That's it. That's the whole job. Flush the vibes, close the fd, say goodnight 💅

👑 RETURN VALUE 👑

• If it ate? 🎉 You get 0 back. Successful completion, come through.
• If it did not eat? You get EOF back, and errno is set to tell you what went wrong.

⚠️ and here's the part you need to tattoo on your brain, fr fr: in either case, any further access to that stream — including calling fclose() on it again — is undefined behavior. She's closed. She's done. Do not touch her. Not even a little. 😭

💀 ERRORS 💀

• EBADF — the file descriptor sitting underneath stream is not valid. It's giving fake ID energy.

Also, fclose() can lowkey fail and set errno for any of the errors specified for close(2), write(2), or fflush(3). So if you're confused, go check those pages, bestie 🫶

🌈 ATTRIBUTES 🌈

For the full explanation of what these terms even mean, go look at attributes(7).

• Interface: fclose()
• Attribute: Thread safety
• Value: MT-Safe ✅

she's thread safe!! she's out here handling multiple threads and never once making it weird. we stan 🧚

⭐ STANDARDS ⭐

C11, POSIX.1-2008.

🍓 HISTORY 🍓

C89, POSIX.1-2001.

she's been doing this since before most of us were born, no cap.

🌸 NOTES 🌸

Important little tea spill: fclose() only flushes the user-space buffers that the C library provides. That's it. That's all she does.

If you actually need your data physically stored on disk, the kernel buffers have to be flushed too — for example with sync(2) or fsync(2). Don't skip this step unless you enjoy losing data, because the vibe check on "where did my file go" is absolutely brutal 💀

🔥 SEE ALSO 🔥

• close(2)
• fcloseall(3)
• fflush(3)
• fileno(3)
• fopen(3)
• setbuf(3)

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and that's the page!! this one came from Linux man-pages 6.20, dated 2025-09-21 — so you know it's fresh, you know it's accurate, you know it ate 💅✨ bye bestie, go close your streams responsibly!! 🦋💖