ShutdownBlockReasonQuery function (winuser.h)

Article
02/22/2024

Retrieves the reason string set by the ShutdownBlockReasonCreate function.

Syntax

BOOL ShutdownBlockReasonQuery(
  [in]            HWND   hWnd,
  [out, optional] LPWSTR pwszBuff,
  [in, out]       DWORD  *pcchBuff
);

Parameters

[in] hWnd

A handle to the main window of the application.

[out, optional] pwszBuff

A pointer to a buffer that receives the reason string. If this parameter is NULL, the function retrieves the number of characters in the reason string.

[in, out] pcchBuff

A pointer to a variable that specifies the size of the pwszBuff buffer, in characters. If the function succeeds, this variable receives the number of characters copied into the buffer, including the null-terminating character. If the buffer is too small, the variable receives the required buffer size, in characters, not including the null-terminating character.

Return value

If the call succeeds, the return value is nonzero.

If the call fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

This function can only be called from the thread that created the window specified by the hWnd parameter. Otherwise, the function fails and the last error code is ERROR_ACCESS_DENIED.

Examples

The following example retrieves the required buffer size, allocates memory for the reason string, retrieves the reason string, and displays the string as debug output.

#include <windows.h>

#pragma comment(lib, "User32.lib")

HWND hWnd;

BOOL DisplayShutdownBlockReason()
{
    DWORD cch=0;

    if (ShutdownBlockReasonQuery(hWnd, NULL, &cch)) 
    { 
        WCHAR *pch = (WCHAR *)LocalAlloc(LMEM_FIXED, cch * sizeof(*pch)); 
        if (NULL != pch) 
        { 
            if (ShutdownBlockReasonQuery(hWnd, pch, &cch)) 
            { 
                OutputDebugStringW(L"Shutdown block reason: "); 
                OutputDebugStringW(pch); 
                OutputDebugStringW(L"\n"); 
            } 
            LocalFree(pch); 
            return TRUE;
        } 
    }
    return FALSE;
}

Requirements

Requirement	Value
Minimum supported client	Windows Vista [desktop apps \| UWP apps]
Minimum supported server	Windows Server 2008 [desktop apps \| UWP apps]
Target Platform	Windows
Header	winuser.h (include Windows.h)
Library	User32.lib
DLL	User32.dll

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