WM_IME_COMPOSITION

Sent two bytes of composition characters to the application. The WM_IME_COMPOSITION message is sent when an IME changes composition status as a result of a user's keystroke. The IME user interface window changes its appearance when it processes this message. An application can call ImmGetCompositionString to obtain detailed composition status.

There is no return value.

wParam

Double byte character that is the latest change of composition character.

lParam

Flag that indicates how the composition string or character changed. An application checks this to retrieve the necessary information. It can be a combination of the following values:

GCS_COMPSTR

GCS_COMPATTR

GCS_COMPCLAUSE

GCS_COMPREADSTR

GCS_COMPREADATTR

GCS_COMPREADCLAUSE

GCS_TYPINGINFO

GCS_SETCURSORPOS

GCS_RESULTSTR

GCS_RESULTCLAUSE

GCS_RESULTREADSTR

GCS_RESULTREADCLAUSE

GCR_ERRORSTR

GCR_INFOSTR

The following values are special styles for WM_IME_COMPOSITION.

Value	Meaning
CS_INSERTCHAR	An IME specifies this value when wParam shows a composition character which should be inserted into the current insertion point. An application should display a composition character if it processes this bit flag.
CS_NOMOVECARET	An IME specifies this value to prevent an application from moving the caret position as a result of processing WM_IME_COMPOSITION. For example, if an IME specifies a combination of CS_INSERTCHAR and CS_NOMOVECARET, it means that an application should insert a character given by wParam into the current caret position, but should not move the caret. Subsequent WM_IME_COMPOSITION with GCS_RESULTSTR replaces this character.

Value

Meaning

CS_INSERTCHAR

An IME specifies this value when wParam shows a composition character which should be inserted into the current insertion point. An application should display a composition character if it processes this bit flag.

CS_NOMOVECARET

An IME specifies this value to prevent an application from moving the caret position as a result of processing WM_IME_COMPOSITION. For example, if an IME specifies a combination of CS_INSERTCHAR and CS_NOMOVECARET, it means that an application should insert a character given by wParam into the current caret position, but should not move the caret. Subsequent WM_IME_COMPOSITION with GCS_RESULTSTR replaces this character.

An application that needs to display composition characters by itself should not pass this message to either the application IME user interface window or DefWindowProc, which passes the message to the default IME window. An IME should give this message to an application even when the IME simply cancels the current composition. An application or IME UI should use this message to erase the current composition string.