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Strn(3)			   Library Functions Manual		       Strn(3)

NAME
       Strncpy(), Strncat() - Safe string copying functions

SYNOPSIS
       cc -I/usr/src/include . . . -L/usr/src/lib -lStrn

       #include	<string.h>
       #include	<Strn.h>

       char *Strncpy(char *dst,	char *src, size_t max);

       char *Strncat(char *dst,	char *src, size_t max);

DESCRIPTION
       The  Strn  library  provides bounds-safe	versions of string copying and
       concatenation functions.	 These are useful with fixed length  character
       arrays because the functions will not overwrite past the	end of the ar-
       ray, unlike strcat or strncat.  The functions  also  guarantee  that  a
       string is nul-terminated, unlike	strncpy	or strncat.

       For example:

	    char bar1[8], foo[8], bar2[8];

       In the following	block, Strncpy correctly sets this to "hello w", using
       seven characters	+ a nul	terminator, so the array is full and  nul-ter-
       minated.

	    Strncpy(foo, "hello	world",	sizeof(foo));

       strncpy	will  write  8 characters, but it won't	nul-terminate.	If you
       tried to	print "foo" you	would get "hello wo" and garbage.

	    strncpy(foo, "hello	world",	sizeof(foo));

       These cooperate to guarantee that the bounds of "foo" are not violated.
       Here, you would get "hello" and then "hello w".

	    Strncpy(foo, "hello", sizeof(foo));
	    Strncat(foo, " world", sizeof(foo));

       These two would overflow, with this usage.  The strncpy would work, but
       then the	strncat	would happily write past the end of foo.

	    strncpy(foo, "hello", sizeof(foo));
	    strncat(foo, " world", sizeof(foo));

       To get the result I want, I would have to do this, which	with  all  the
       extra overhead in the third argument is unacceptable.

	    strncpy(foo, "hello", sizeof(foo));
	    strncat(foo, " world", sizeof(foo) - strlen(foo) - 1);

       In actual use, you don't	usually	call Strncpy or	Strncat	directly.  The
       library's header	file includes two macros which fill in the third argu-
       ment  with  sizeof(dst)	for you.  That way, they can be	used as	direct
       replacements of strcpy and strcat most of the time:

	    char fullName[32];

	    strcpy(fullName, firstName);
	    strcat(fullName, " ");
	    strcat(fullName, lastName);

       This can	be transformed into the	following, and you  can	 rest  assured
       that  you won't trash the stack if for some reason "firstName" +	"last-
       Name" would exceed the bounds of	"fullName."

	    STRNCPY(fullName, firstName);
	    STRNCAT(fullName, "	");
	    STRNCAT(fullName, lastName);

SEE ALSO
       strcpy(3), strncpy(3), strcat(3), strncat(3), sprintf(3).

West Interactive Corporation					       Strn(3)

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO

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