strncat(9)

💅 strncat(9)

okay so this is a page from the Kernel API Manual and bestie, we need to talk about strncat. it's a whole situation. grab a snack. 🍓

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🌸 NAME 🌸

strncat — append a string to an existing string

like, the sequel to the string. the string part 2. the string electric boogaloo.

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✨ SYNOPSIS ✨

        char * strncat (char * const p , const char * const q , __kernel_size_t
       count );

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🎀 ARGUMENTS 🎀

• p — pointer to a NUL-terminated string, and this is the one you're appending to. the main character, honestly. 👑
• q — pointer to the source string you're appending from. the supporting role that still gets screentime.
• count — the maximum number of bytes to read from q. it's giving boundaries. we love boundaries. 🦋

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💖 DESCRIPTION 💖

so what it does: it appends at most count bytes from q (and it stops at the first NUL byte, no cap) after the NUL-terminated string at p. and p will be NUL-terminated. periodt. 💅

and then it returns p. that's it. that's the whole thing.

⚠️ okay so now the serious part, and i need you to actually listen: do not use this function. like, at all. not me being dramatic, it's literally on the page.

here's the tea — while FORTIFY_SOURCE tries to avoid read and write overflows, that's only possible when the sizes of p and q are known to the compiler. so if the compiler doesn't know? no protection. none. 😭

instead, prefer building the string with formatting, via scnprintf or similar. that's the vibe. that's the move. 🫶

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🌈 SEE ALSO 🌈

• Kernel file ./include/linux/fortify-string.h
• unsafe_memcpy(9)
• strnlen(9)
• strlen(9)
• strlcat(9)
• strcat(9)
• strcpy(9)

the whole string function friend group, basically. they all show up to the group chat. 🧚

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and that's the page, bestie! this one came out of ./include/linux in October 2026 — so like, remember to check that date if you're citing it, because nothing's more embarrassing than citing a stale manpage. 💀 anyway ily, go use scnprintf, and stay safe out there. 🌸💜