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Linux 2.6 - man page for strncat (linux section 3)

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

NAME
       strcat, strncat - concatenate two strings

SYNOPSIS
       #include <string.h>

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

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

DESCRIPTION
       The strcat() function appends the src string to the dest string, overwriting the terminat-
       ing null byte ('\0') at the end of dest, and then  adds	a  terminating	null  byte.   The
       strings	may  not  overlap, and the dest string must have enough space for the result.  If
       dest is not large enough,  program  behavior  is  unpredictable;  buffer  overruns  are	a
       favorite avenue for attacking secure programs.

       The strncat() function is similar, except that

       *  it will use at most n bytes from src; and

       *  src does not need to be null-terminated if it contains n or more bytes.

       As with strcat(), the resulting string in dest is always null-terminated.

       If  src	contains n or more bytes, strncat() writes n+1 bytes to dest (n from src plus the
       terminating null byte).	Therefore, the size of dest must be at least strlen(dest)+n+1.

       A simple implementation of strncat() might be:

	   char*
	   strncat(char *dest, const char *src, size_t n)
	   {
	       size_t dest_len = strlen(dest);
	       size_t i;

	       for (i = 0 ; i < n && src[i] != '\0' ; i++)
		   dest[dest_len + i] = src[i];
	       dest[dest_len + i] = '\0';

	       return dest;
	   }

RETURN VALUE
       The strcat() and strncat() functions return a pointer to the resulting string dest.

CONFORMING TO
       SVr4, 4.3BSD, C89, C99.

NOTES
       Some systems (the BSDs, Solaris, and others) provide the following function:

	   size_t strlcat(char *dest, const char *src, size_t size);

       This function appends the null-terminated string src to the string dest, copying  at  most
       size-strlen(dest)-1  from  src,	and  adds a null terminator to the result, unless size is
       less than strlen(dest).	This function fixes the buffer overrun problem of  strcat(),  but
       the caller must still handle the possibility of data loss if size is too small.	The func-
       tion returns the length of the string strlcat() tried to create; if the	return	value  is
       greater	than or equal to size, data loss occurred.  If data loss matters, the caller must
       either check the arguments before the call, or test the function return value.	strlcat()
       is  not	present  in glibc and is not standardized by POSIX, but is available on Linux via
       the libbsd library.

SEE ALSO
       bcopy(3), memccpy(3), memcpy(3), strcpy(3), string(3), strncpy(3), wcscat(3), wcsncat(3)

COLOPHON
       This page is part of release 3.55 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					STRCAT(3)


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