#ifndef _NTRTL_H
NTSYSAPI
NTSTATUS
NTAPI
RtlMultiByteToUnicodeN(
_Out_writes_bytes_to_(MaxBytesInUnicodeString, *BytesInUnicodeString) PWCH UnicodeString,
_In_ ULONG MaxBytesInUnicodeString,
_Out_opt_ PULONG BytesInUnicodeString,
_In_reads_bytes_(BytesInMultiByteString) PCSTR MultiByteString,
_In_ ULONG BytesInMultiByteString
);
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This function is documented in Windows Driver Kit.