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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 (''), 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] != ''; i++)
                   dest[i] = src[i];
               for ( ; i < n; i++)
                   dest[i] = '';

               return dest;
           }

RETURN VALUE

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

ATTRIBUTES

   Multithreading (see pthreads(7))
       The strcpy() and strncpy() functions are thread-safe.

CONFORMING TO

       SVr4, 4.3BSD, C89, C99.

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 target 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:

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

       (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.)

       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  target 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

       This  page  is  part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



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