RtlInitEmptyAnsiString - NtDoc

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

// Strings

FORCEINLINE
VOID
NTAPI
RtlInitEmptyAnsiString(
    _Out_ PANSI_STRING AnsiString,
    _Pre_maybenull_ _Pre_readable_size_(MaximumLength) PCHAR Buffer,
    _In_ USHORT MaximumLength
    )
{
    memset(AnsiString, 0, sizeof(ANSI_STRING));
    AnsiString->MaximumLength = MaximumLength;
    AnsiString->Buffer = Buffer;
}

#endif

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This function is documented in Windows Driver Kit.