RtlUnicodeStringToUTF8String - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers

#ifndef _NTRTL_H
#if (PHNT_VERSION >= PHNT_20H1)

NTSYSAPI
NTSTATUS
NTAPI
RtlUnicodeStringToUTF8String(
    _Inout_ PUTF8_STRING DestinationString,
    _In_ PCUNICODE_STRING SourceString,
    _In_ BOOLEAN AllocateDestinationString
    );

#endif
#endif
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This function is documented in Windows Driver Kit here and here.

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