make_relative_filename(3)

💖 make_relative_filename — the Allegro manual, but make it make sense 💖

okay bestie, this one lives in the Allegro game programming library, and it's genuinely so useful once you get the vibe. no cap. 🫶

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✨ NAME ✨

make_relative_filename — she tries to make a relative filename out of an absolute path and an absolute filename. part of the Allegro game programming library, periodt. 💅

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🌸 SYNOPSIS 🌸

#include <allegro.h>

char *make_relative_filename(char *dest, const char *path, const char
*filename, int size);

like. look at her. iconic signature fr fr. 🎀

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🦋 DESCRIPTION 🦋

so what she's doing is: you hand her an absolute path and an absolute filename, and she attempts to cook up a relative filename for you, storing at most size bytes into the dest buffer. that's the whole assignment. she ate. 🔥

⚠️ two things you NEED to know before you go off, bestie: - she won't work if the paths aren't canonical under the current platform — go check canonicalize_filename() for that, iykyk - dest cannot be used as the input value for path or filename. do not do it. it's giving chaos. 😭

here's the example, verbatim, don't touch her:

char base[] = "/long/absolute/path/program.exe";
char user_input[] = "/nice/and/short.txt";
...
make_relative_filename(buf, base, user_input, sizeof(buf));
/* Under Unix buf would contain:
   ../../../nice/and/short.txt */

the way that ../../../nice/and/short.txt is literally a glow-up from that giant absolute path... we love a transformation arc. ✨👑

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💜 RETURN VALUE 💜

she returns a copy of the dest parameter when she succeeds. if she fails, you get NULL. 🫠

and lowkey the failure case is messy — for example, under DOS, if one path starts with "C:\" and another starts with "A:\", bestie there is simply no relative path between those two worlds. two different drives, two different universes. 💀

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🌈 SEE ALSO 🌈

• make_absolute_filename(3) — the reverse girly 🎀
• is_relative_filename(3) — the vibe check ✅
• canonicalize_filename(3) — go here first if your paths are acting uncanonical 🙈

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that's the whole page, bestie — no notes, she's perfect. this little love letter comes straight out of the Allegro manual, version 4.4.3, and the page you just read is make_relative_filename(3). go forth and compute, queen. 💖✨🌸🦋👑💅