strcpy(3)

✨ strcpy — the girlies' guide to string copy/catenate ✨

okay bestie, welcome to the strcpy(3) page 💖 this is strcpy and strcat from the Linux man-pages, and yes we're doing the whole thing, no skips, no cap.

---

🌸 NAME 🌸

strcpy, strcat — string copy/catenate

📚 LIBRARY 📚

Standard C library (libc, -lc) — she lives in libc, that's her home 🏠

🔥 SYNOPSIS 🔥

#include <string.h>

char *strcpy(char *restrict dst, const char *restrict src);
char *strcat(char *restrict dst, const char *restrict src);

💅 DESCRIPTION 💅

strcpy()

okay so this one copies the string pointed to by src into a string at the buffer pointed to by dst. 🫶

and here's the part everyone ignores and then cries about later: the programmer is responsible for allocating a destination buffer large enough, that is, strlen(src) + 1. that + 1 is for the null byte bestie, do not forget the null byte 😭

it is equivalent to:

stpcpy(dst, src), dst

strcat()

this one catenates the string pointed to by src after the string pointed to by dst (overwriting its terminating null byte). so it's like, scooting over and letting src move in ✨

again, the programmer is responsible for allocating a destination buffer large enough, that is, strlen(dst) + strlen(src) + 1. yes you need both lengths. yes you need the + 1. no you cannot skip it 🙈

it is equivalent to:

stpcpy(strnul(dst), src), dst

---

🎀 RETURN VALUE 🎀

these functions return dst. that's it, that's the whole return value. she gives you back your own pointer, iconic behaviour honestly 👑

🦋 ATTRIBUTES 🦋

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

• Interface: strcpy(), strcat()
• Attribute: Thread safety
• Value: MT-Safe

so like, she's MT-Safe, meaning the girlies can run her from multiple threads and she won't start drama 🌈

⭐ STANDARDS ⭐

C11, POSIX.1-2008.

📜 HISTORY 📜

POSIX.1-2001, C89, SVr4, 4.3BSD. she's been around, she's a legacy queen 💜

💀 CAVEATS 💀

⚠️ the strings src and dst may not overlap. not even a little. do not do it.

⚠️ if the destination buffer is not large enough, the behavior is undefined. that's UB bestie, that's the scary one, that's the one that gives you a segfault at 3am with no stack trace 😭 see _FORTIFY_SOURCE in feature_test_macros(7) if you want the compiler to at least side-eye you about it.

---

🌟 EXAMPLES 🌟

here's the whole girl, verbatim, every line 🫶

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

int
main(void)
{
    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()");

    strcpy(buf1, "Hello ");
    strcat(buf1, "world");
    strcat(buf1, "!");
    len = strlen(buf1);

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

    exit(EXIT_SUCCESS);
}

see how she computed size with all the strlens plus the + 1 and then malloc'd exactly that much? that's the whole vibe check in one code block. ate. 🔥

👀 SEE ALSO 👀

stpcpy(3), strdup(3), string(3), wcscpy(3), string_copying(7)

---

that's the page bestie, go forth and always allocate enough bytes 🎀✨💖

this was fun — Linux man-pages 6.20, dated 2026-08-03, mwah 💋