VB中利用winsock控件，TCP协议实现多客户端连接
1 通信程序通常都是采用Client/Server形式。这就要求作为服务器的主机可以同时处理多个客户的请求。因此在编写服务器程序时要添加多个Winsock控件。在开始我们先加入两个Winsock控件。其中一个用来侦听网上请求信号，取名为Listener；另外一个为初始的连接口，取名叫Sock（0）。注意，后一个控件要设为动态数组的形式，以后当客户增多时，可在这个控件基础上动态增加。由于受资源限制，我们在本例中设定最多可以同时接纳15个客户。客户机一般只与一个主机相连，因此程序只须一个Winsock进行连接就足够了。这个程序要用到的控件较少，除了Winsock和Form控件外，只须再添加Commmand控件即可。下面是具体程序和详细注释。
2 ******************************
3 '服务器程序
4 ******************************
5 Option Explicit
6 定义常量
7 Const BUSY As Boolean = False
8 Const FREE As Boolean = True
9 定义连接状态
10 Dim ConnectState() As Boolean
11 Private Sub Form_Load()
12 ReDim Preserve ConnectState(0 To 1)
13 On Error Resume Next
14 ConnectState(0) = FREE
15 ConnectState(1) = FREE
16 '指定网络端口号
17 Listener.LocalPort = 1011
18 '开始侦听
19 Listener.Listen
20 End Sub
21 Private Sub Listener_ConnectionRequest(ByVal requestID As Long)
22 Dim SockIndex As Integer
23 Dim SockNum As Integer
24 On Error Resume Next
25 Form1.Print requestID & "连接请求"
26 '查找连接的用户数
27 SockNum = UBound(ConnectState)
28 If SockNum > 14 Then
29 Form1.Print SockIndex & ""
30 Exit Sub
31 End If
32 '查找空闲的sock
33 SockIndex = FindFreeSocket()
34 '如果已有的sock都忙，而且sock数不超过15个，动态添加sock
35 If SockIndex > SockNum Then
36 Load Sock(SockIndex)
37 End If
38 ConnectState(SockIndex) = BUSY
39 Sock(SockIndex).Tag = SockIndex
40 '接受请求
41 Sock(SockIndex).Accept (requestID)
42 Form1.Print SockIndex & "接受请求"
43 End Sub
44
45 '客户断开，关闭相应的sock
46 Private Sub Sock_Close(Index As Integer)
47 If Sock(Index).State <> sckClosed Then
48 Sock(Index).Close
49 End If
50 ConnectState(Index) = FREE
51 Form1.Print Index & "close"
52 End Sub
53
54 '接收数据
55 Private Sub Sock_DataArrival(Index As Integer, ByVal bytesTotal As Long)
56 Dim dx As Double
57 Form1.Print "数据来自" & Index
58 Sock(Index).GetData dx, vbDouble
59 Form1.Print "dx=" & dx
60 End Sub
61
62 '寻找空闲的sock
63 Public Function FindFreeSocket()
64 Dim SockCount, i As Integer
65 SockCount = UBound(ConnectState)
66 For i = 0 To SockCount
67 If ConnectState(i) = FREE Then
68 FindFreeSocket = i
69 Exit Function
70 End Ifs
71 Next i
72 ReDim Preserve ConnectState(0 To SockCount + 1)
73 FindFreeSocket = UBound(ConnectState)
74 End Function
75
76 ***************************
77 '客户程序
78 ’***************************
79 Option Explicit
80 '发送数据
81 Private Sub command1_Click()
82 Dim dx As Double
83 dx = 23.9
84 sock.SendData dx
85 MsgBox ("data sended")
86 End Sub
87
88 Private Sub Form_Load()
89 '远程主机名
90 sock.RemoteHost = "media2"
91 '网络端口
92 sock.RemotePort = 1011
93 '发出连接命令
94 sock.Connect
95 Command1.Enabled = False
96 End Sub
97
98 '服务器关闭
99 Private Sub sock_Close()
100 MsgBox ("socket closed")
101 End Sub
102
103 '连接成功
104 Private Sub sock_Connect()
105 MsgBox ("socket connected")
106 Command1.Enabled = True
107 End Sub