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STRLCPY(3)	       FreeBSD Library Functions Manual		    STRLCPY(3)

NAME
     strlcpy, strlcat -- size-bounded string copying and concatenation

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <string.h>

     size_t
     strlcpy(char * restrict dst, const	char * restrict	src, size_t size);

     size_t
     strlcat(char * restrict dst, const	char * restrict	src, size_t size);

DESCRIPTION
     The strlcpy() and strlcat() functions copy	and concatenate	strings
     respectively.  They are designed to be safer, more	consistent, and	less
     error prone replacements for strncpy(3) and strncat(3).  Unlike those
     functions,	strlcpy() and strlcat()	take the full size of the buffer (not
     just the length) and guarantee to NUL-terminate the result	(as long as
     size is larger than 0 or, in the case of strlcat(), as long as there is
     at	least one byte free in dst).  Note that	a byte for the NUL should be
     included in size.	Also note that strlcpy() and strlcat() only operate on
     true ``C''	strings.  This means that for strlcpy()	src must be NUL-termi-
     nated and for strlcat() both src and dst must be NUL-terminated.

     The strlcpy() function copies up to size -	1 characters from the NUL-ter-
     minated string src	to dst,	NUL-terminating	the result.

     The strlcat() function appends the	NUL-terminated string src to the end
     of	dst.  It will append at	most size - strlen(dst)	- 1 bytes, NUL-termi-
     nating the	result.

RETURN VALUES
     The strlcpy() and strlcat() functions return the total length of the
     string they tried to create.  For strlcpy() that means the	length of src.
     For strlcat() that	means the initial length of dst	plus the length	of
     src.  While this may seem somewhat	confusing, it was done to make trunca-
     tion detection simple.

     Note however, that	if strlcat() traverses size characters without finding
     a NUL, the	length of the string is	considered to be size and the destina-
     tion string will not be NUL-terminated (since there was no	space for the
     NUL).  This keeps strlcat() from running off the end of a string.	In
     practice this should not happen (as it means that either size is incor-
     rect or that dst is not a proper ``C'' string).  The check	exists to pre-
     vent potential security problems in incorrect code.

EXAMPLES
     The following code	fragment illustrates the simple	case:

	   char	*s, *p,	buf[BUFSIZ];

	   ...

	   (void)strlcpy(buf, s, sizeof(buf));
	   (void)strlcat(buf, p, sizeof(buf));

     To	detect truncation, perhaps while building a pathname, something	like
     the following might be used:

	   char	*dir, *file, pname[MAXPATHLEN];

	   ...

	   if (strlcpy(pname, dir, sizeof(pname)) >= sizeof(pname))
		   goto	toolong;
	   if (strlcat(pname, file, sizeof(pname)) >= sizeof(pname))
		   goto	toolong;

     Since it is known how many	characters were	copied the first time, things
     can be sped up a bit by using a copy instead of an	append

	   char	*dir, *file, pname[MAXPATHLEN];
	   size_t n;

	   ...

	   n = strlcpy(pname, dir, sizeof(pname));
	   if (n >= sizeof(pname))
		   goto	toolong;
	   if (strlcpy(pname + n, file,	sizeof(pname) -	n) >= sizeof(pname) - n)
		   goto	toolong;

     However, one may question the validity of such optimizations, as they
     defeat the	whole purpose of strlcpy() and strlcat().  As a	matter of
     fact, the first version of	this manual page got it	wrong.

SEE ALSO
     snprintf(3), strncat(3), strncpy(3), wcslcpy(3)

HISTORY
     The strlcpy() and strlcat() functions first appeared in OpenBSD 2.4, and
     made their	appearance in FreeBSD 3.3.

FreeBSD	10.1			 June 22, 1998			  FreeBSD 10.1

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | SEE ALSO | HISTORY

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