ChangeDisplaySettingsExA function (winuser.h)

Article
02/09/2023

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

Note Apps that you design to target Windows 8 and later can no longer query or set display modes that are less than 32 bits per pixel (bpp); these operations will fail. These apps have a compatibility manifest that targets Windows 8. Windows 8 still supports 8-bit and 16-bit color modes for desktop apps that were built without a Windows 8 manifest; Windows 8 emulates these modes but still runs in 32-bit color mode.

Syntax

LONG ChangeDisplaySettingsExA(
  [in] LPCSTR   lpszDeviceName,
  [in] DEVMODEA *lpDevMode,
       HWND     hwnd,
  [in] DWORD    dwflags,
  [in] LPVOID   lParam
);

Parameters

[in] lpszDeviceName

A pointer to a null-terminated string that specifies the display device whose graphics mode will change. Only display device names as returned by EnumDisplayDevices are valid. See EnumDisplayDevices for further information on the names associated with these display devices.

The lpszDeviceName parameter can be NULL. A NULL value specifies the default display device. The default device can be determined by calling EnumDisplayDevices and checking for the DISPLAY_DEVICE_PRIMARY_DEVICE flag.

[in] lpDevMode

A 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 must be initialized to the size, in bytes, of the DEVMODE structure. The dmDriverExtra member must be initialized to indicate the number of bytes of private driver data following the DEVMODE structure. In addition, you can use any 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	Position of the device in a multi-monitor 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 settings.

Value	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	Use the dmPosition value.

hwnd

Reserved; must be NULL.

[in] dwflags

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. 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.
CDS_VIDEOPARAMETERS	When set, the lParam parameter is a pointer to a VIDEOPARAMETERS structure.
CDS_ENABLE_UNSAFE_MODES	Enables settings changes to unsafe graphics modes.
CDS_DISABLE_UNSAFE_MODES	Disables settings changes to unsafe graphics modes.

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

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.

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.

[in] lParam

If dwFlags is CDS_VIDEOPARAMETERS, lParam is a pointer to a VIDEOPARAMETERS structure. Otherwise lParam must be NULL.

Return value

The ChangeDisplaySettingsEx function returns one of the following values.

Return code	Description
DISP_CHANGE_SUCCESSFUL	The settings change was successful.
DISP_CHANGE_BADDUALVIEW	The settings change was unsuccessful because the 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	Unable to write settings to the registry.
DISP_CHANGE_RESTART	The computer must be restarted for the graphics mode to work.

Remarks

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

When adding a display monitor to a multiple-monitor system programmatically, set DEVMODE.dmFields to DM_POSITION and specify a position (in DEVMODE.dmPosition) for the monitor you are adding that is adjacent to at least one pixel of the display area of an existing monitor. To detach the monitor, set DEVMODE.dmFields to DM_POSITION but set DEVMODE.dmPelsWidth and DEVMODE.dmPelsHeight to zero. For more information, see Multiple Display Monitors.

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

To change the settings for more than one display at the same time, first call ChangeDisplaySettingsEx for each device individually to update the registry without applying the changes. Then call ChangeDisplaySettingsEx once more, with a NULL device, to apply the changes. For example, to change the settings for two displays, do the following:


ChangeDisplaySettingsEx (lpszDeviceName1, lpDevMode1, NULL, (CDS_UPDATEREGISTRY | CDS_NORESET), NULL);
ChangeDisplaySettingsEx (lpszDeviceName2, lpDevMode2, NULL, (CDS_UPDATEREGISTRY | CDS_NORESET), NULL);
ChangeDisplaySettingsEx (NULL, NULL, NULL, 0, NULL);

DPI Virtualization

This API does not participate in DPI virtualization. The input given is always in terms of physical pixels, and is not related to the calling context.

Note

The winuser.h header defines ChangeDisplaySettingsEx as an alias which automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	winuser.h (include Windows.h)
Library	User32.lib
DLL	User32.dll
API set	ext-ms-win-ntuser-sysparams-ext-l1-1-1 (introduced in Windows 10, version 10.0.14393)

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