IsWow64Message function (winuser.h)

Determines whether the last message read from the current thread's queue originated from a WOW64 process.

Syntax

BOOL IsWow64Message();

Return value

The function returns TRUE if the last message read from the current thread's queue originated from a WOW64 process, and FALSE otherwise.

Remarks

This function is useful to helping you develop 64-bit native applications that can receive private messages sent from 32-bit client applications, if the messages are associated with data structures that contain pointer-dependent data. In these situations, you can call this function in your 64-bit native application to determine if the message originated from a WOW64 process and then thunk the message appropriately.

Examples

For compatibility with operating systems that do not support this function, call GetProcAddress to detect whether IsWow64Message is implemented in User32.dll. If GetProcAddress succeeds, it is safe to call this function. Otherwise, WOW64 is not present. Note that this technique is not a reliable way to detect whether the operating system is a 64-bit version of Windows because the User32.dll in current versions of 32-bit Windows also contains this function.

#include <windows.h>
#include <tchar.h>

typedef BOOL (WINAPI *LPFN_ISWOW64MESSAGE) (void);

LPFN_ISWOW64MESSAGE fnIsWow64Message;

BOOL IsWow64Msg()
{
    // IsWow64Message is not available on all supported versions of Windows
    // Use LoadLibrary to ensure that the DLL containing the function is loaded
    // and GetProcAddress to get a pointer to the function if available.

    fnIsWow64Message = (LPFN_ISWOW64MESSAGE) GetProcAddress(
        LoadLibrary(TEXT("user32")), "IsWow64Message");
  
    if (NULL != fnIsWow64Message)
    {        
        return (fnIsWow64Message());
    }
    else return FALSE;
}

int main( void )
{
    if(IsWow64Msg())
    {
        _tprintf(TEXT("The last message was from a 32-bit process.\n"));
    }
    else if (NULL == fnIsWow64Message )
    {
        _tprintf(TEXT("The IsWow64Message function is not available (%d).\n"), GetLastError());
    }
    else 
    {
        _tprintf(TEXT("The last message was from a 64-bit process.\n"));
    }
    return 0;
}

Requirements

Requirement	Value
Minimum supported client	Windows Vista, Windows XP with SP2 [desktop apps only]
Minimum supported server	Windows Server 2008, Windows Server 2003 with SP1 [desktop apps only]
Target Platform	Windows
Header	winuser.h (include Windows.h)
Library	User32.lib
DLL	User32.dll

See also

GetNativeSystemInfo

IsWow64Process

WOW64