WinStationSendMessageW - NtDoc

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

// rev
NTSYSAPI
BOOLEAN
NTAPI
WinStationSendMessageW(
    _In_opt_ HANDLE ServerHandle,
    _In_ ULONG SessionId,
    _In_ PCWSTR Title,
    _In_ ULONG TitleLength,
    _In_ PCWSTR Message,
    _In_ ULONG MessageLength,
    _In_ ULONG Style,
    _In_ ULONG Timeout,
    _Out_ PULONG Response,
    _In_ BOOLEAN DoNotWait
    );

#endif

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This function is a wrapper over an RPC method documented in the [MS-TSTS] specification.