kstrtoul(9)

💖 kstrtoul — like, the kstrtoul(9) girlies' field guide 💖

Okay bestie, so this one is from the Kernel API Manual (that's the section 9 energy, kernel-internals only, iykyk), and it's genuinely one of the most useful little functions ever. It's called kstrtoul and it literally converts a string into an unsigned long. That's it. That's the whole vibe. ✨

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✨ NAME ✨

kstrtoul — convert a string to an unsigned long 🌸

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🦋 SYNOPSIS 🦋

int kstrtoul (const char *s , unsigned int base , unsigned long *res );

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🎀 ARGUMENTS 🎀

• s — the start of the string. And no, it can't just be any string, she has RULES: the string must be null-terminated, and it may also include a single newline before its terminating null. The first character may also be a plus sign, but not a minus sign. Not even a little minus sign. Nope. 🙈
• base — the number base to use. The maximum supported base is 16. But here's the iconic part: if base is given as 0, then the base of the string is automatically detected with the conventional semantics, like she's reading your mind:
  • if it begins with 0x, the number will be parsed as a hexadecimal (case insensitive 👑)
  • if it otherwise begins with 0, it will be parsed as an octal number
  • otherwise it will be parsed as a decimal
• res — where to write the result of the conversion on success. That's the drop spot. 🫶

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🔥 DESCRIPTION 🔥

So the returns, bestie, listen up:

• 0 on success 🎉
• -ERANGE on overflow 💀
• -EINVAL on parsing error 😭

She's preferred over simple_strtoul — like, that's the whole point, she's the upgraded main character version. ✨

And the return code must be checked. That is not optional. Not "oh I'll get to it later". Check it. The kernel will not be sending you a friendly little follow-up message, she will just break. 🚨

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🌈 SEE ALSO 🌈

• Kernel file ./include/linux/kstrtox.h
• kstrtol(9)

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okay that's the whole page, no cap, you got this 🧚💜

Signed off from the ./include/linux corner of the kernel, October 2026 edition — mwah, go check your return codes, ily, byeeee 💅🎀🌟