按DEL键竞不发送WM_CHAR消息，而发送WM_KEYDOWN消息，还有消息中的第一个参数是虚拟键值，第二个参数不知干什么的？?

[yongdu]

[Jackzhu]

Value of lParam. Specifies the repeat count, scan code, extended-key flag, context code, previous key-state flag, and transition-state flag, as shown in the following table. Value Description
0–15 Specifies the repeat count for the current message. The value is the number of times the keystroke is auto-repeated 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 Specifies the scan code. The value depends on the original equipment manufacturer (OEM).
24 Specifies 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 Specifies the context code. The value is always 0 for a WM_KEYDOWN message.
30 Specifies 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 Specifies the transition state. The value is always 0 for a WM_KEYDOWN message

[929]

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

WM_CHAR是在WM_KEYDOWN以后发生，其间WINDOWS经过TranslateMessage调用，对按键进行了解释。而DEL在解释后，被滤掉了。
在LPARAM中传送lKeyData，代表当消息传送时，这个按键的重复次数（因为WINDOWS消息循环没有实时传递按键消息），扫描码（SCAN CODE），以及扩展键标志。及ALT等键的状态。


0-15 Specifies the repeat count. The value is the number of times the keystroke is repeated as a result of the user holding down the key.
16-23 Specifies the scan code. The value depends on the original equipment manufacturer (OEM).
24 Specifies 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 Specifies 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 Specifies 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 Specifies the transition state. The value is 1 if the key is being released, or it is 0 if the key is being pressed.

[Shania]

很简单：
WM_CHAR:只接受ASCII码，区分大小写
WM_KEYDOWN:接受VIRTUAL KEY，（include 光标，DEL...），不区分大小写！
第二个参数是一个32位的数，每一位或几位都代表了一些键盘的设置状态：
0-15位：按键延迟的时间
16-23位：指定扫描码，主要和OEM厂商有关
24位：值为1时代表这是一个扩展码（不在标准101，102键盘上的）
25-28位：不用
29位：WM_KEYDOWN时，为0
30位：前一个键的状态（DWON OR UP）
31位：WM_KEYDOWN时，为0