Nonsystem Character Messages

A window procedure can receive four different character messages, including WM_CHAR, WM_DEADCHAR, WM_SYSCHAR, and WM_SYSDEADCHAR. The TranslateMessage function generates a WM_CHAR or WM_DEADCHAR message when it processes a WM_KEYDOWN message. Similarly, it generates a WM_SYSCHAR or WM_SYSDEADCHAR message when it processes a WM_SYSKEYDOWN message.

An application that processes keyboard input typically ignores all but the WM_CHAR message, passing any other messages to the DefWindowProc function. Windows uses the WM_SYSCHAR and WM_SYSDEADCHAR messages to implement menu mnemonics.

The wParam parameter of all character messages contains the character code of the character key that was pressed. The value of the character code depends on the window class of the window receiving the message. If the Unicode version of the RegisterClass function was used to register the window class, the system provides Unicode characters to all windows of that class. Otherwise, the system provides ASCII character codes from the Windows character set. For more information about Unicode, see Unicode and Character Sets.

The contents of the lParam parameter of a character message are identical to the contents of the lParam parameter of the key-down message that was translated to produce the character message. For information about the contents of the lParam parameter, see Keystroke Message Flags.

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