STRCPY(3)						     Linux Programmer's Manual							 STRCPY(3)

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.

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 over-
       flowed 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.  You can force termi-
       nation using something like the following:

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

       (Of course, the above technique ignores the fact that information contained in src 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: pro-
       grams 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 3.53 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/.

GNU
								    2012-07-19								 STRCPY(3)