WM_CHAR message

Artykuł
08/04/2022

Posted to the window with the keyboard focus when a WM_KEYDOWN message is translated by the TranslateMessage function. The WM_CHAR message contains the character code of the key that was pressed.

#define WM_CHAR                         0x0102

Parameters

wParam

The character code of the key.

lParam

The repeat count, scan code, extended-key flag, context code, previous key-state flag, and transition-state flag, as shown in the following table.

Bits	Meaning
0-15	The repeat count for the current message. The value is the number of times the keystroke is autorepeated as a result of the user holding down the key. If the keystroke is held long enough, multiple messages are sent. However, the repeat count is not cumulative.
16-23	The scan code. The value depends on the OEM.
24	Indicates whether the key is an extended key, such as the right-hand ALT and CTRL keys that appear on an enhanced 101- or 102-key keyboard. The value is 1 if it is an extended key; otherwise, it is 0.
25-28	Reserved; do not use.
29	The context code. The value is 1 if the ALT key is held down while the key is pressed; otherwise, the value is 0.
30	The previous key state. The value is 1 if the key is down before the message is sent, or it is 0 if the key is up.
31	The transition state. The value is 1 if the key is being released, or it is 0 if the key is being pressed.

For more detail, see Keystroke Message Flags.

Return value

An application should return zero if it processes this message.

Example

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
   
    // ...

    case WM_CHAR:
        OnKeyPress(wParam);
        break;

    default:
        return DefWindowProc(hwnd, message, wParam, lParam);
    }
    return 0;
}

Example from Windows Classic Samples on GitHub.

Remarks

The WM_CHAR message uses UTF-16 (16-bit Unicode Transformation Format) code units in its wParam if the Unicode version of the RegisterClass function was used to register the window class. Otherwise, the system provides characters in the current process code page, which can be set to UTF-8 in Windows Version 1903 (May 2019 Update) and newer. For more information, see Registering Window Classes and Use UTF-8 code pages in Windows apps.

Starting with Windows Vista, WM_CHAR message can send UTF-16 surrogate pairs to Unicode windows. Use the IS_HIGH_SURROGATE, IS_LOW_SURROGATE, and IS_SURROGATE_PAIR macros to detect such cases, if necessary.

There is not necessarily a one-to-one correspondence between keys pressed and character messages generated, and so the information in the high-order word of the lParam parameter is generally not useful to applications. The information in the high-order word applies only to the most recent WM_KEYDOWN message that precedes the posting of the WM_CHAR message.

For enhanced 101- and 102-key keyboards, extended keys are the right ALT and the right CTRL keys on the main section of the keyboard; the INS, DEL, HOME, END, PAGE UP, PAGE DOWN and arrow keys in the clusters to the left of the numeric keypad; and the divide (/) and ENTER keys in the numeric keypad. Some other keyboards may support the extended-key bit in the lParam parameter.

The WM_UNICHAR message is the same as WM_CHAR, except it uses UTF-32. It is designed to send or post Unicode characters to ANSI windows, and it can handle Unicode Supplementary Plane characters.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Header	Winuser.h (include Windows.h)