ZOPEN(3)

💖 ZOPEN(3) — compressed stream open function 💖

okay so real talk, this is from the Library Functions Manual and it's about zopen, which is literally the moment your compressed file gets a whole FILE stream to itself. bestie, it's giving "fopen but make it compressed" and honestly? obsessed. let's get into it 🫶

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✨ SYNOPSIS ✨

#include "zopen.h"

FILE *
zopen(const char *path, const char *mode, int bits);

three args, one header, zero drama. slay.

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🌸 DESCRIPTION 🌸

so zopen() opens the compressed file whose name is the string pointed to by path, and it associates a stream with it. that's the whole vibe. your file, your stream, iconic behavior 💅

the argument mode points to one of these one-character strings, and you only get to pick from this lil list:

• "r" — open the compressed file for reading ✨ the stream is positioned at the beginning of the file. very demure, very start-of-file.
• "w" — truncate the file to zero length, or create a compressed file for writing 🔥 the stream is positioned at the beginning of the file too. yes, it will absolutely nuke what was there — that's the "truncate to zero length" part, no cap.

any files that get created will have mode "S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH" (that's 0666), as modified by the process' umask value (peep umask(2) for the details, iykyk).

💀 important vibe check: files may only be read or written. seek operations are not allowed. like, at all. don't try it, she's not that kind of stream.

the bits argument, if it's non-zero, is set to the bits code limit ⭐ if it's zero, the default is 16. see compress(1) if you want the full lore on that one.

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🎀 RETURN VALUES 🎀

upon successful completion, zopen() returns a FILE pointer 💖 it ate, no crumbs.

otherwise, NULL is returned and the global variable errno is set to indicate the error 😭 not the ending we wanted but it's honest.

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🦋 ERRORS 🦋

here's the breakdown of what can go wrong, and bestie, it happens:

• [EINVAL] — the mode or bits arguments specified to zopen() were invalid 🙈 like, wrong input, wrong energy.
• [EFTYPE] — the compressed file starts with an invalid header, or the compressed file is compressed with more bits than can be handled 💀 she looked at the file and said "I can't work with this."

also, fair warning — zopen() may also fail and set errno for any of the errors specified for the routines fopen(3) or funopen(3) 🌈 so it's not just the errors listed above, it can catch hands from those too.

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🧚 SEE ALSO 🧚

compress(1), fopen(3), funopen(3)

(the holy trinity, fr fr 🫶)

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👑 HISTORY 👑

the zopen function first appeared in 4.4BSD ⭐ a true elder, a main character with lore.

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🌈 BUGS 🌈

⚠️ the zopen() function may not be portable to systems other than BSD. so if you're out here on some other system expecting her to work, that's a sorry bestie moment 😭 not undefined behavior exactly, just... not portable. plan accordingly.

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💜 okay that's the whole page! zopen — compressed stream open function, from the Library Functions Manual, was published by Debian on June 9, 1993. a vintage queen. stay compressed, stay hydrated, and remember: read or write only, no seeking 🎀✨