char *strncat(char *restrict s1, const char *restrict s2, size_t n);
IEEE Std 1003.1-2017
strncat() function shall append not more than n bytes (a
NUL character and bytes that follow it are not
appended) from the array pointed to by s2 to the end of the string pointed to by s1. The initial byte of s2
NUL character at the end of s1. A terminating NUL character is always appended to the result. If copying
takes place between objects that overlap, the behavior is undefined.
strncat() function shall return s1; no return value shall be reserved to indicate an error.
No errors are defined.