strcpy(3)                  Library Functions Manual                  strcpy(3)

NAME
       strcpy, strcat - copy or catenate a string

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <string.h>

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

DESCRIPTION
       strcpy()
              This function copies the string pointed to by src, into a string
              at the buffer pointed to by dst.  The programmer is responsible
              for allocating a destination buffer large enough, that is,
              strlen(src) + 1.

              It is equivalent to

                  stpcpy(dst, src), dst

       strcat()
              This function catenates the string pointed to by src, after the
              string pointed to by dst (overwriting its terminating null
              byte).  The programmer is responsible for allocating a
              destination buffer large enough, that is, strlen(dst) +
              strlen(src) + 1.

              It is equivalent to

                  stpcpy(strnul(dst), src), dst

RETURN VALUE
       These functions return dst.

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

       +--------------------------------------------+---------------+---------+
       |Interface                                   | Attribute     | Value   |
       +--------------------------------------------+---------------+---------+
       |strcpy (), strcat ()                        | Thread safety | MT-Safe |
       +--------------------------------------------+---------------+---------+
STANDARDS
       C11, POSIX.1-2008.

HISTORY
       POSIX.1-2001, C89, SVr4, 4.3BSD.

CAVEATS
       The strings src and dst may not overlap.

       If the destination buffer is not large enough, the behavior is
       undefined.  See _FORTIFY_SOURCE in feature_test_macros(7).

       strcat() can be very inefficient.  Read about Shlemiel the painter
       <https://www.joelonsoftware.com/2001/12/11/back-to-basics/>.

EXAMPLES
       #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 ALSO
       stpcpy(3), strdup(3), string(3), wcscpy(3), string_copying(7)

Linux man-pages 6.18              2026-02-25                         strcpy(3)