\nJust because you write default:\n return DefWindowProc(…);\n}\n<\/PRE>\n \nThe above code fragment doesn’t handle the case WM_SOMETHING:\n if (wParam == 4) { DoSomething4(…); }\n else … ????? …\n return 0;<\/FONT><\/p>\n default:\n return DefWindowProc(…);\n}\n<\/PRE>\n \nIf the value is 4, then you do your special “something 4” processing,\nbut what about all the other values? How do you handle them?\n<\/P>\n \nWell, think about it: How did you handle them before?\nThe original code, before you added a case WM_SOMETHING:\n return DefWindowProc(…);<\/FONT><\/p>\n default:\n return DefWindowProc(…);\n}\n<\/PRE>\n \nIn the original code, since there was no explicit handler for\nthe case WM_SOMETHING:\n if (wParam == 4) return DefWindowProc(…);\n else return DefWindowProc(…);<\/FONT><\/p>\n default:\n return DefWindowProc(…);\n}\n<\/PRE>\n \nBecause if the \nOf course, I expanded the block in precisely this way so it matches\nup with the case we started writing when we decided to handle the\n case WM_SOMETHING:\n if (wParam == 4) { DoSomething4(…); }\n else return DefWindowProc(…);<\/FONT>\n return 0;<\/p>\n default:\n return DefWindowProc(…);\n}\n<\/PRE>\ncase WM_SOMETHING:<\/CODE> doesn’t mean\nthat you have to handle all possible parameters for the\nWM_SOMETHING<\/CODE> message.\nYou’re still allowed to call the DefWindowProc<\/CODE> function.\nAfter all, that’s what you did when you didn’t have a\ncase WM_SOMETHING:<\/CODE> statement in the first place.\n<\/P>\n\nswitch (uMsg) {\ncase WM_CHAR:\n OnChar(…);\n return 0;<\/p>\nWM_SOMETHING<\/CODE>\nmessage at all.\nSuppose the WM_SOMETHING<\/CODE> message uses the wParam<\/CODE>\nparameter to specify what type of something occurred, and you\nonly want to override the default processing\nin the case where wParam<\/CODE> has the value of 4.\nWhat do you do with the other values?\n<\/P>\n\nswitch (uMsg) {\ncase WM_CHAR:\n OnChar(…);\n return 0;<\/p>\nWM_SOMETHING<\/CODE>\nhandler, was equivalent to this:\n<\/P>\n\nswitch (uMsg) {\ncase WM_CHAR:\n OnChar(…);\n return 0;<\/p>\nWM_SOMETHING<\/CODE> message, control is transferred to\nthe default<\/CODE> case handler, which just calls the\nDefWindowProc<\/CODE> function.\nIf you really want to, you can expand the case out a bit more:\n<\/P>\n\nswitch (uMsg) {\ncase WM_CHAR:\n OnChar(…);\n return 0;<\/p>\nwParam<\/CODE> is 4, the original code just\ncalled DefWindowProc<\/CODE>.\nAnd if the wParam<\/CODE> was something other than 4,\nthe original code still just\ncalled DefWindowProc<\/CODE>.\n<\/P>\nWM_SOMETHING<\/CODE> method.\nWritten out this way, it becomes obvious\nwhat to write for the question marks.\n<\/P>\n\nswitch (uMsg) {\ncase WM_CHAR:\n OnChar(…);\n return 0;<\/p>\n