XLIB Programming Manual, Rel. 5, Third Edition

11.10 Getting Composed Text

Prior to R5, XLookupString() was used to convert the keycode returned in a KeyPress event into a KeySym and further into a character string that could be passed to the X text drawing functions. Unfortunately, this function only works for the Latin-1 charset. To support internationalization in a limited way, there were alternate LookupString functions in the Xmu library: XmuLookupLatin2(), XmuLookupJISX0201(), XmuLookupGreek(), etc. In R5, these have been superseded by XmbLookupString() and XwcLookupString(). These functions are identical except in the type of string they return: the Xmb version returns a multi-byte string of char, and Xwc version returns a wide-character string of wchar_t. In both cases the string will be encoded as appropriate for the locale of the IC.^[47]

Whenever a KeyPress event is delivered to an application that is performing internationalized text input, the application should use that event in a call to XmbLookupString() or XwcLookupString(). (Note that KeyRelease events should not be passed to these functions—they will result in undefined behavior.) The application should not expect that each call to Xmb/XwcLookupString() will return a string. Depending on the complexity of the input method in use, a user may type many keystrokes before any composed input is ready for the application. Neither should the application expect that Xmb/XwcLookupString() will return a single character at a time—in some input methods a user may type ...