Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help 
STRCAT(3)		     Library Functions Manual		       STRCAT(3)

NAME
     strcat, strncat -- concatenate strings

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <string.h>

     char *
     strcat(char * restrict s, const char * restrict append);

     char *
     strncat(char * restrict s, const char * restrict append, size_t count);

DESCRIPTION
     The  strcat()  and strncat() functions append a copy of the null-terminated
     string append to the end of the null-terminated string s, then add a termi-
     nating `\0'.  The string s must have sufficient space to hold  the  result.
     If s and append overlap, the results are undefined.

     The  strncat() function appends not more than count characters from append,
     and then adds a terminating `\0'.	If s and append overlap, the results are
     undefined.

RETURN VALUES
     The strcat() and strncat() functions return the pointer s.

SEE ALSO
     bcopy(3), memccpy(3), memcpy(3), memmove(3), strcpy(3),  strlcat(3),  strl-
     cpy(3), wcscat(3)

STANDARDS
     The   strcat()   and  strncat()  functions  conform  to  ISO/IEC  9899:1990
     ("ISO C90").

HISTORY
     The  strcat()  function  first  appeared  in  the	Programmer's   Workbench
     (PWB/UNIX)  and was ported to Version 7 AT&T UNIX; strncat() first appeared
     in Version 7 AT&T UNIX.

SECURITY CONSIDERATIONS
     The strcat() function is easily misused in a manner which enables malicious
     users to arbitrarily change a running  program's  functionality  through  a
     buffer overflow attack.

     Avoid  using strcat().  Instead, use strncat() or strlcat() and ensure that
     no more characters are copied to the destination buffer than it can hold.

     Note that strncat() can also be problematic.  It may be a security  concern
     for  a  string to be truncated at all.  Since the truncated string will not
     be as long as the original, it may refer to a completely different resource
     and usage of the truncated resource could result in very  incorrect  behav-
     ior.  Example:

     void
     foo(const char *arbitrary_string)
     {
	     char onstack[8];

     #if defined(BAD)
	     /*
	      * This first strcat is bad behavior.  Do not use strcat!
	      */
	     (void)strcat(onstack, arbitrary_string);	     /* BAD! */
     #elif defined(BETTER)
	     /*
	      * The following two lines demonstrate better use of
	      * strncat().
	      */
	     (void)strncat(onstack, arbitrary_string,
		 sizeof(onstack) - strlen(onstack) - 1);
     #elif defined(BEST)
	     /*
	      * These lines are even more robust due to testing for
	      * truncation.
	      */
	     if (strlen(arbitrary_string) + 1 >
		 sizeof(onstack) - strlen(onstack))
		     err(1, "onstack would be truncated");
	     (void)strncat(onstack, arbitrary_string,
		 sizeof(onstack) - strlen(onstack) - 1);
     #endif
     }

FreeBSD ports 15.quarterly	  April 3, 2022 		       STRCAT(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=strcat&sektion=3&manpath=FreeBSD+15.1-RELEASE+and+Ports.quarterly>

home | help