The ChangeDisplaySettings function changes the settings of the default display device to the graphics mode specified in lpDevMode. To change the settings of a specified display device, use the ChangeDisplaySettingsEx function.
LONG ChangeDisplaySettings(
LPDEVMODE lpDevMode,
DWORD dwflags
);
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, Windows NT 5.0 and later: Position of the device in a multi-monitor configuration |
In addition to setting a value in one or more of the preceding DEVMODE members, you must also set the appropriate flags in the dmFields member. The flags indicate which members of the DEVMODE structure are used for the display settings change. If the appropriate bit is not set in dmFields, the display setting will not be changed. Set one or more of the following flags:
| Flag | 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, Windows NT 5.0 and later: Use the dmPosition value. |
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.
| Flag | Meaning |
|---|---|
| 0 | The graphics mode for the current screen will be changed dynamically. |
| 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_TEST | The system tests if the requested graphics mode could be set. |
| CDS_FULLSCREEN | The mode is temporary in nature. Windows NT: 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_SET_PRIMARY | This device will become the primary device. |
| CDS_RESET | The settings should be changed, even if the requested settings are the same as the current settings. |
| CDS_NORESET | The settings will be saved in the registry, but will not take affect. This flag is only valid when specified with the CDS_UPDATEREGISTRY flag. |
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: 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.
The ChangeDisplaySettings function returns one of the following values.
| Value | Meaning |
|---|---|
| DISP_CHANGE_SUCCESSFUL | The settings change was successful. |
| DISP_CHANGE_RESTART | The computer must be restarted in order for the graphics mode to work. |
| DISP_CHANGE_BADFLAGS | An invalid set of flags was passed in. |
| 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_BADMODE | The graphics mode is not supported. |
| DISP_CHANGE_NOTUPDATED | Windows NT: Unable to write settings to the registry. |
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 NT: Requires version 3.5 or later.
Windows: Requires Windows 95 or later.
Windows CE: Unsupported.
Header: Declared in winuser.h.
Import Library: Use user32.lib.
Unicode: Implemented as Unicode and ANSI versions on Windows NT.
Device Contexts Overview, Device Context Functions, ChangeDisplaySettingsEx, CreateDC, DEVMODE, EnumDisplayDevices, EnumDisplaySettings, WM_DISPLAYCHANGE