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NAME

       strcpy, strncpy - copy a string

SYNOPSIS

       #include <string.h>

       char *strcpy(char *dest, const char *src);

       char *strncpy(char *dest, const char *src, size_t n);

DESCRIPTION

       The strcpy() function copies the string pointed to by src, including the terminating null byte ('\0'), to
       the  buffer  pointed  to  by  dest.  The strings may not overlap, and the destination string dest must be
       large enough to receive the copy.  Beware of buffer overruns!  (See BUGS.)

       The strncpy() function is similar, except that at most n bytes of src are copied.  Warning: If  there  is
       no null byte among the first n bytes of src, the string placed in dest will not be null-terminated.

       If  the  length  of  src  is less than n, strncpy() writes additional null bytes to dest to ensure that a
       total of n bytes are written.

       A simple implementation of strncpy() might be:

           char *
           strncpy(char *dest, const char *src, size_t n)
           {
               size_t i;

               for (i = 0; i < n && src[i] != '\0'; i++)
                   dest[i] = src[i];
               for ( ; i < n; i++)
                   dest[i] = '\0';

               return dest;
           }

RETURN VALUE

       The strcpy() and strncpy() functions return a pointer to the destination string dest.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).
       ┌─────────────────────┬───────────────┬─────────┐
       │ InterfaceAttributeValue   │
       ├─────────────────────┼───────────────┼─────────┤
       │ strcpy(), strncpy() │ Thread safety │ MT-Safe │
       └─────────────────────┴───────────────┴─────────┘

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

NOTES

       Some programmers consider strncpy() to be inefficient and error prone.  If the  programmer  knows  (i.e.,
       includes  code  to  test!)  that the size of dest is greater than the length of src, then strcpy() can be
       used.

       One valid (and intended) use of strncpy() is to copy a C string to a fixed-length buffer  while  ensuring
       both  that  the  buffer  is not overflowed and that unused bytes in the destination buffer are zeroed out
       (perhaps to prevent information leaks if the buffer is to be written to media or transmitted  to  another
       process via an interprocess communication technique).

       If  there  is  no  terminating  null byte in the first n bytes of src, strncpy() produces an unterminated
       string in dest.  If buf has length buflen, you can force termination using something like the following:

           if (buflen > 0) {
               strncpy(buf, str, buflen - 1);
               buf[buflen - 1]= '\0';
           }

       (Of course, the above technique ignores the fact that,  if  src  contains  more  than  buflen - 1  bytes,
       information is lost in the copying to dest.)

   strlcpy()
       Some systems (the BSDs, Solaris, and others) provide the following function:

           size_t strlcpy(char *dest, const char *src, size_t size);

       This  function  is  similar  to  strncpy(),  but  it  copies  at most size-1 bytes to dest, always adds a
       terminating null byte, and does not pad the destination with (further) null bytes.  This  function  fixes
       some  of the problems of strcpy() and strncpy(), but the caller must still handle the possibility of data
       loss if size is too small.  The return value  of  the  function  is  the  length  of  src,  which  allows
       truncation  to  be  easily  detected:  if  the  return value is greater than or equal to size, truncation
       occurred.  If loss of data matters, the caller must either check the arguments before the call,  or  test
       the  function  return  value.  strlcpy() is not present in glibc and is not standardized by POSIX, but is
       available on Linux via the libbsd library.

BUGS

       If the destination string of a strcpy() is not large enough, then  anything  might  happen.   Overflowing
       fixed-length  string  buffers is a favorite cracker technique for taking complete control of the machine.
       Any time a program reads or copies data into a buffer, the program first  needs  to  check  that  there's
       enough  space.   This  may  be  unnecessary  if you can show that overflow is impossible, but be careful:
       programs can get changed over time, in ways that may make the impossible possible.

SEE ALSO

       bcopy(3), memccpy(3), memcpy(3), memmove(3),  stpcpy(3),  stpncpy(3),  strdup(3),  string(3),  wcscpy(3),
       wcsncpy(3)

COLOPHON

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       information  about  reporting  bugs,  and  the  latest  version  of  this   page,   can   be   found   at
       https://www.kernel.org/doc/man-pages/.

GNU                                                2019-03-06                                          STRCPY(3)