BSON_APPEND_UNDEFINED(3)

💅 BSON_APPEND_UNDEFINED 💅

okay so this is a page straight out of libbson (that's BSON_APPEND_UNDEFINED(3) if you're being formal, bestie) and it's literally all about sticking an undefined value into a BSON doc. tiny page, big lore. let's get into it 🫶

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✨ SYNOPSIS ✨

here's the whole vibe, verbatim, no cap:

#define BSON_APPEND_UNDEFINED(b, key) \
   bson_append_undefined (b, key, (int) strlen (key))

bool
bson_append_undefined (bson_t *bson, const char *key, int key_length);

so you've got your cute little convenience macro up top, and the real function underneath. the macro just does the strlen math for you so you don't have to 💖

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🎀 PARAMETERS 🎀

• bson — a bson_t. that's your document, the main character of this whole operation 👑
• key — an ASCII C string holding the name of the field. yep, ASCII specifically, don't get cute with it 🙈
• key_length — how long key is, in bytes. OR you can pass -1 and it'll figure the length out itself using strlen(). lazy girl friendly ✨

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🦋 DESCRIPTION 🦋

so bson_append_undefined() shall append a brand new element to bson, and that element is of type BSON_TYPE_UNDEFINED. slay, new element acquired 💅

and here's the tea: undefined is common in Javascript. like, extremely common. it's giving ubiquitous.

BUT — and this is the important part, don't skip it — this element type is deprecated and should not be used in new code. i'm serious. do not bring it into new code. leave it in the past where it belongs 💀

🚨 real talk: deprecated = don't use it in new code. it's right there in the text, bestie. i don't make the rules.

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🌈 RETURNS 🌈

returns true if the operation was applied successfully. periodt. ✨

it will fail if appending the value grows bson larger than INT32_MAX. that's the hard ceiling, no negotiating 🔥

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🌸 AUTHOR 🌸

MongoDB, Inc — the icons themselves 👑

🎀 COPYRIGHT 🎀

2009-present, MongoDB, Inc.

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okay that's the whole page, you ate that 🍓 go forth and maybe... not use undefined in new code? just a thought 💜

<div align="center">⭐ libbson 2.5.6 · Oct 09, 2026 · mwah, bye bestie 🦋</div>