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### 6.19 `wcsncpy`—copy part of a wide-character string

Synopsis

         #include <wchar.h>
         wchar_t *wcsncpy(wchar_t *__restrict s1,
             const wchar_t *__restrict s2, size_t n);

Description
The `wcsncpy` function copies not more than n wide-character codes (wide-character codes that follow a null wide-character code are not copied) from the array pointed to by s2 to the array pointed to by s1. If copying takes place between objects that overlap, the behaviour is undefined. Note that if s1 contains more than n wide characters before its terminating null, the result is not null-terminated.

If the array pointed to by s2 is a wide-character string that is shorter than n wide-character codes, null wide-character codes are appended to the copy in the array pointed to by s1, until n wide-character codes in all are written.

Returns
The `wcsncpy` function returns s1; no return value is reserved to indicate an error.

Portability
ISO/IEC 9899; POSIX.1.

No supporting OS subroutines are required.