ChangeDisplaySettings

The ChangeDisplaySettings function changes the settings of the default display device to the specified graphics mode.

To change the settings of a specified display device, use the ChangeDisplaySettingsEx function.

[in] Pointer to a DEVMODE structure that describes the new graphics mode. If lpDevMode is NULL, all the values currently in the registry will be used for the display setting. Passing NULL for the lpDevMode parameter and 0 for the dwFlags parameter is the easiest way to return to the default mode after a dynamic mode change.

The dmSize member of DEVMODE must be initialized to the size, in bytes, of the DEVMODE structure. The dmDriverExtra member of DEVMODE must be initialized to indicate the number of bytes of private driver data following the DEVMODE structure. In addition, you can use any or all of the following members of the DEVMODE structure.

Member	Meaning
dmBitsPerPel	Bits per pixel
dmPelsWidth	Pixel width
dmPelsHeight	Pixel height
dmDisplayFlags	Mode flags
dmDisplayFrequency	Mode frequency
dmPosition	Windows 98/Me, Windows 2000/XP: Position of the device in a multimonitor configuration

In addition to using one or more of the preceding DEVMODE members, you must also set one or more of the following values in the dmFields member to change the display setting.

Member	Meaning
DM_BITSPERPEL	Use the dmBitsPerPel value.
DM_PELSWIDTH	Use the dmPelsWidth value.
DM_PELSHEIGHT	Use the dmPelsHeight value.
DM_DISPLAYFLAGS	Use the dmDisplayFlags value.
DM_DISPLAYFREQUENCY	Use the dmDisplayFrequency value.
DM_POSITION	Windows 98/Me, Windows 2000/XP: Use the dmPosition value.

[in] Indicates how the graphics mode should be changed. This parameter can be one of the following values.

Value	Meaning
0	The graphics mode for the current screen will be changed dynamically.
CDS_FULLSCREEN	The mode is temporary in nature. Windows NT/2000/XP: If you change to and from another desktop, this mode will not be reset.
CDS_GLOBAL	The settings will be saved in the global settings area so that they will affect all users on the machine. Otherwise, only the settings for the user are modified. This flag is only valid when specified with the CDS_UPDATEREGISTRY flag.
CDS_NORESET	The settings will be saved in the registry, but will not take effect. This flag is only valid when specified with the CDS_UPDATEREGISTRY flag.
CDS_RESET	The settings should be changed, even if the requested settings are the same as the current settings.
CDS_SET_PRIMARY	This device will become the primary device.
CDS_TEST	The system tests if the requested graphics mode could be set.
CDS_UPDATEREGISTRY	The graphics mode for the current screen will be changed dynamically and the graphics mode will be updated in the registry. The mode information is stored in the USER profile.

Specifying CDS_TEST allows an application to determine which graphics modes are actually valid, without causing the system to change to that graphics mode.

If CDS_UPDATEREGISTRY is specified and it is possible to change the graphics mode dynamically, the information is stored in the registry and DISP_CHANGE_SUCCESSFUL is returned. If it is not possible to change the graphics mode dynamically, the information is stored in the registry and DISP_CHANGE_RESTART is returned.

Windows NT/2000/XP: If CDS_UPDATEREGISTRY is specified and the information could not be stored in the registry, the graphics mode is not changed and DISP_CHANGE_NOTUPDATED is returned.

Value	Meaning
DISP_CHANGE_SUCCESSFUL	The settings change was successful.
DISP_CHANGE_BADDUALVIEW	Windows XP: The settings change was unsuccessful because system is DualView capable.
DISP_CHANGE_BADFLAGS	An invalid set of flags was passed in.
DISP_CHANGE_BADMODE	The graphics mode is not supported.
DISP_CHANGE_BADPARAM	An invalid parameter was passed in. This can include an invalid flag or combination of flags.
DISP_CHANGE_FAILED	The display driver failed the specified graphics mode.
DISP_CHANGE_NOTUPDATED	Windows NT/2000/XP: Unable to write settings to the registry.
DISP_CHANGE_RESTART	The computer must be restarted in order for the graphics mode to work.

To ensure that the DEVMODE structure passed to ChangeDisplaySettings is valid and contains only values supported by the display driver, use the DEVMODE returned by the EnumDisplaySettings function.

When the display mode is changed dynamically, the WM_DISPLAYCHANGE message is sent to all running applications with the following message parameters.

Parameters	Meaning
wParam	New bits per pixel
LOWORD(lParam)	New pixel width
HIWORD(lParam)	New pixel height

Windows 95/98/Me: If the calling thread has any windows, ChangeDisplaySettings sends them the WM_DISPLAYCHANGE message immediately (for windows in all other threads, the message is sent when the thread can receive nonqueued messages). This may cause the shell to get its message too soon and could squash icons. To avoid this problem, have ChangeDisplaySettings do resolution switching by calling on a thread with no windows, for example, a new thread.

Windows 95/98/Me: ChangeDisplaySettingsW is supported by the Microsoft Layer for Unicode.