RtlUnicodeToUTF8N - NtDoc

#ifndef _NTRTL_H
#if (PHNT_VERSION >= PHNT_WIN7)

NTSYSAPI
NTSTATUS
NTAPI
RtlUnicodeToUTF8N(
    _Out_writes_bytes_to_(UTF8StringMaxByteCount, *UTF8StringActualByteCount) PCHAR UTF8StringDestination,
    _In_ ULONG UTF8StringMaxByteCount,
    _Out_opt_ PULONG UTF8StringActualByteCount,
    _In_reads_bytes_(UnicodeStringByteCount) PCWCH UnicodeStringSource,
    _In_ ULONG UnicodeStringByteCount
    );

#endif
#endif
View code on GitHub