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The Windows Sockets ActiveX control and the TCP Server ActiveX control in the Distinct
Visual Internet Toolkit - 32 require that all data sent or received must be
defined as a string. Other Visual Basic predefined data types and user defined data types
cannot be sent or received. Instead, user defined data types (structures) must be
converted (copied) into strings before sending them and strings must be converted (copied)
into structures after receiving them.
To allow this conversion of structures to strings and strings to structures, Distinct
Visual Internet Toolkit - 32 supplies the "DSTRCT32.DLL" library. The
"T32-107 Disk 1" diskette contains this file in the DSTRUCT
subdirectory. Copy this file to the directory which contains the Distinct program files
(ActiveX controls) on your hard drive. The CopyStruct function in
"DSTRCT32.DLL" is used for the conversion and must be declared in a Visual Basic
application as follows.
- Declare Function CopyStruct Lib "DSTRCT32.DLL" (ByVal Dst
As Any, ByVal Src As Any, ByVal Length As Long) As Integer.
For predefined data types, the above declaration is sufficient. The declaration has to
be modified for user defined data types (structures). For each user defined structure, the
CopyStruct function must be declared twice (each time under a different name)
and both declarations must be aliased to the CopyStruct function. Each
function declaration specifies the type of conversion (converting a structure to a string
or converting a string to a structure).
For example, the following two declarations are necessary for the user defined
structure MyStruct.
- Declare Function CopyStruct1 Lib "DSTRCT32.DLL" Alias
"CopyStruct" (ByVal Dst As Any, Src As MyStruct, ByVal
Length As Long) As Integer
- Declare Function CopyStruct2 Lib "DSTRCT32.DLL" Alias
"CopyStruct" (Dst As MyStruct, ByVal Src As Any, ByVal
Length As Long) As Integer
CopyStruct1 is an alias of the CopyStruct function to
specifically copy MyStruct to a string. Similarly, CopyStruct2
is an alias of the CopyStruct function to specifically copy a string to MyStruct.
To Send a Structure
1. Convert the structure to a string using the CopyStruct function.
The Src parameter is the structure to copy.
The Dst parameter is the string.
The Length parameter is the exact number of bytes to copy from the Src
parameter.
2. Assign the Dst parameter string to the Send property of the custom
control.
To Receive a Structure
1. Assign the Receive property of the custom control to a string.
2. Convert the string to a structure using the CopyStruct function.
The Src parameter is the string to copy.
The Dst parameter is the structure.
The Length parameter is the exact number of bytes to copy from the Src
parameter.
Note
The CopyStruct function can be used to copy any data type to a string and
vice versa. The data type can be an Integer, a Long, a user defined structure or even
another string. Aliases of the CopyStruct function are only required for user
defined structures and data types.
Example
The following example describes the usage of the CopyStruct function:
- Type MyStruct1 ' user defined type 1
- CustNum As Long
- CustName As String * 40
- End Type
- Type MyStruct2 ' user defined type 2
- Index As Integer
- Value As Long
- End Type
- ' generic declaration
- Declare Function CopyStruct Lib "DSTRCT32.DLL" (ByVal Dst As Any, ByVal Src As
Any, ByVal Length As Long) As Integer
- ' declarations for MyStruct1
- Declare Function CopyStruct1 Lib "DSTRCT32.DLL" Alias "CopyStruct"
(ByVal Dst As Any, Src As MyStruct1, ByVal Length As Long) As Integer
- Declare Function CopyStruct2 Lib "DSTRCT32.DLL" Alias "CopyStruct"
(Dst As MyStruct1, ByVal Src As Any, ByVal Length As Long) As Integer
- ' declarations for MyStruct2
- Declare Function CopyStruct3 Lib "DSTRCT32.DLL" Alias "CopyStruct"
(ByVal Dst As Any, Src As MyStruct2, ByVal Length As Long) As Integer
- Declare Function CopyStruct4 Lib "DSTRCT32.DLL" Alias "CopyStruct"
(Dst As MyStruct2, ByVal Src As Any, ByVal Length As Long) As Integer
- sub Convert ()
- Dim Send1 As MyStruct1
- Dim Recv1 As MyStruct1
- Dim Send2 As MyStruct2
- Dim Recv2 As MyStruct2
- Dim Msg As String * 50
- Dim ret, bytes As Integer
- Send1.CustNum = 123456 ' to send the structure
- Send1.CustName = "Nobody"
- bytes = Len(Send1)
- ret = CopyStruct1(Msg, Send1, bytes)
- Socket.Send = Msg
- Msg = Socket.Receive ' to receive the structure
- bytes = Socket.Result
- ret = CopyStruct2(Recv1, Msg, bytes)
- Send2.Index = 10 ' convert MyStruct2
- Send2.Value = 135
- bytes = Len(Send2)
- ret = CopyStruct3(Msg, Send2, bytes)
- ret = CopyStruct4(Recv2, Msg, bytes)
- End Sub
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