stpcpy(3)

💖 stpcpy — string return-offset-pointer copy 💖

okay bestie so this is stpcpy(3), a libc baddie from the Standard C library (libc, -lc). yes the library name is lowkey just "libc, -lc". she's that girl. ✨

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✨ SYNOPSIS ✨

#include <string.h>

char *stpcpy(char *restrict dst, const char *restrict src);

so you include <string.h>, and you get stpcpy() which takes a dst (restrict) and an src (restrict), and hands you back a char *. slay.

🎀 Feature Test Macro Requirements for glibc 🎀

(if you wanna know the whole vibe behind these, go peek at feature_test_macros(7))

stpcpy():

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

like. glibc really said "you need a macro pass to get in here." 💅

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🌸 DESCRIPTION 🌸

stpcpy() is basically strcpy(3)'s cooler cousin — except instead of returning dst like a normal person, she returns a pointer to the terminating null byte in dst. main character behavior fr fr.

she's equivalent to all of these expressions, no cap:

memset(mempcpy(dst, src, strlen(src)), '\0', 1);
strcpy(mempcpy(dst, src, strlen(src)), "");
strcpy(dst, src) + strlen(src)

like, literally the same thing three ways. pick your fighter. 🔥

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🫶 RETURN VALUE 🫶

she returns a pointer to the terminating null byte of the copied string. so not the start of dst, bestie — the end. the null byte. the little '\0' that finishes the sentence. iconic.

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👑 ATTRIBUTES 👑

if you're like "wait what do these terms even mean," that's what attributes(7) is for. go read it, i'll wait. 🍓

• stpcpy()
  • Thread safety: MT-Safe

so she's thread safe, we love a function that doesn't start drama. 🧚

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⭐ STANDARDS ⭐

POSIX.1-2008.

🌈 HISTORY 🌈

POSIX.1-2008.

(same energy both times, she's consistent, periodt.)

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💅 EXAMPLES 💅

here's the whole thing, copy it exactly, don't be cute with it:

#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int
main(void)
{
    char    *p;
    char    *buf1;
    size_t  len, size;

    size = strlen("Hello ") + strlen("world") + strlen("!") + 1;
    buf1 = malloc(sizeof(*buf1) * size);
    if (buf1 == NULL)
        err(EXIT_FAILURE, "malloc()");

    p = buf1;
    p = stpcpy(p, "Hello ");
    p = stpcpy(p, "world");
    p = stpcpy(p, "!");
    len = p - buf1;

    printf("[len = %zu]: ", len);
    puts(buf1);  // "Hello world!"
    free(buf1);

    exit(EXIT_SUCCESS);
}

see how p keeps marching forward every call? that's the whole point of the returned pointer — you just keep appending and never look back. len = p - buf1; is literally the length. obsessed. 😭💖

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🦋 SEE ALSO 🦋

• strcpy(3)
• string(3)
• wcpcpy(3)
• string_copying(7)

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and that's the tea, bestie 🎀 this page came to you from Linux man-pages 6.20, dated 2026-08-10. stay safe out there, keep your restrict qualifiers on, and remember: the null byte is not a suggestion, it's a lifestyle. byeee 💜✨