strncpy man page on Scientific

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

       strcpy, strncpy - copy a string

       #include <string.h>

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

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

       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.

       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() pads  the	 remainder  of
       dest with null bytes.

       A simple implementation of strncpy() might be:

	   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;

       The  strcpy()  and strncpy() functions return a pointer to the destina‐
       tion string dest.

       SVr4, 4.3BSD, C89, C99.

       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.

       If there is no terminating null byte in the first n characters of  src,
       strncpy()  produces  an unterminated string in dest.  Programmers often
       prevent this mistake by forcing termination as follows:

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

       If the destination string of a strcpy() is not large enough, then  any‐
       thing  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  unneces‐
       sary  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

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

       This page is part of release 3.22 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at

GNU				  2009-06-01			     STRCPY(3)

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