stpncpy(3)

💖 stpncpy(3) — the copy function that actually tells you where it stopped 💖

okay bestie, we're in the Library Functions Manual and the star of today's show is stpncpy(3). she's a char * copier with main character energy and a receipt. let's get into it ✨

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✨ NAME ✨

stpncpy — nonstring return-offset-pointer copy

📚 LIBRARY 📚

Standard C library (libc, -lc)

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🌸 SYNOPSIS 🌸

#include <string.h>  // see memory.h(3head)

char *stpncpy(size_t dsize;
              char dst[restrict dsize], const char *restrict src,
              size_t dsize);

🎀 Feature Test Macro Requirements for glibc 🎀

(peep feature_test_macros(7) if you need the lore)

stpncpy():

• Since glibc 2.10:
  • _POSIX_C_SOURCE >= 200809L
• Before glibc 2.10:
  • _GNU_SOURCE

yes bestie, the rules changed at glibc 2.10, that's just the vibe of it 💅

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💜 DESCRIPTION 💜

So here's the tea. This function is equivalent to strncpy(3) — like, same copy energy — but she does one extra iconic thing: she hands you back a pointer to one past the last nonnull written character. that's it, that's the whole slay. 🔥

She's equivalent to this, fr fr:

memset(mempcpy(dst, src, strnlen(src, dsize)), '\0',
       dsize - strnlen(src, dsize))

like, copy what needs copying, zero-fill the rest, and return the offset. no cap. 🫶

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🦋 RETURN VALUE 🦋

This function returns a pointer to one past the last non-null character written. which is, mathematically:

dest + strnlen(src, n)

that's your answer, that's the address she's pulling up on, periodt. 👑

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⭐ ATTRIBUTES ⭐

For an explanation of the terms used in this section, see attributes(7).

• Interface → stpncpy()
  • Attribute → Thread safety
  • Value → MT-Safe

MT-Safe means she can hang out in threads with all her friends, no drama. 💖

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🌈 STANDARDS 🌈

POSIX.1-2008.

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🌸 HISTORY 🌸

glibc 1.07. And also POSIX.1-2008. she's been around, and honestly? aging like fine wine. 🍓

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💀 CAVEATS 💀

See strncpy(3).

okay so like — genuinely go read that one bestie, this girl inherits her whole personality from strncpy(3). no skimming!! 😭

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👀 SEE ALSO 👀

• memory.h(3head)
• string_copying(7)

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Linux man-pages 6.20 · 2026-08-10 · mwah, that's a wrap, go forth and copy safely bestie 🎀🦋✨