char *strncat(char *str1
const char *str2
Appends the string pointed to by str2 to the end of
the string pointed to by str1 up to n
characters long. The terminating null character of str1
is overwritten. Copying stops once n characters are
copied or the terminating null character of str2 is
copied. A terminating null character is always appended to
str1. If overlapping occurs, the result is undefined.
The argument str1 is returned.