vsprintf(9)

✨ NAME ✨

vsprintf — bestie, this is the one that takes your format string and your va_list and just slaps the finished string straight into a buffer for you. It's from the Kernel API Manual side of town, section 9 (kernel API, iykyk) 💅

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🎀 SYNOPSIS 🎀

int vsprintf (char *buf , const char *fmt , va_list args );

That's the whole vibe. Three args, one int coming back at you 🦋

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🌸 ARGUMENTS 🌸

• buf — the buffer where the final result gets dropped off. It's giving "the destination", the place the string actually lives 💖
• fmt — the format string you wanna use. This is the one doing all the work, okurrr 🔥
• args — the arguments for that format string, already wrapped up in a va_list 🎁

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🧚 DESCRIPTION 🧚

So the return value? It's the number of characters written into buf, and that count does not include the trailing ' '. Yes, that's literally what the page says, I'm not gonna gaslight you 💀

🚨 Real talk though: use vsnprintf or vscnprintf if you wanna avoid buffer overflows. vsprintf does not know where your buffer ends, and she will keep writing. No cap. That's a whole dangerous situation and you do not want that energy in your kernel 🫶

If you're not already dealing with a va_list, lowkey consider using sprintf instead — it's way less extra ✨

Also, for real, go check the vsnprintf documentation for the format string extensions over C99 — that's where the details live, bestie 👑

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💜 SEE ALSO 💜

• Kernel file ./lib/vsprintf.c 👀
• simple_strtoull(9)
• simple_strtoul(9)
• simple_strtol(9)
• simple_strtoll(9)
• vsnprintf(9)
• vscnprintf(9)
• snprintf(9)
• scnprintf(9)
• sprintf(9)
• vbin_printf(9)
• bstr_printf(9)
• vsscanf(9)
• sscanf(9)

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okay that's the whole page, slay 💅✨

Signed off from ./lib, dated October 2026, and yeah — it's still vsprintf(9) at the bottom, iconic as ever 👑🎀