Creating a Structure and Accessing Data in visual basic 2005

A structure is a user defined type, which is used to hold multiple types of related data and is a generalization of a user defined data type (UDT). In other words, we combine variables of different data types to create a structure and use them when we do not want the additional functionality of an extendable class and when it will not contain large amount of a data. These are a replacement of UDT in visual basic 6.0. Compared to UDTs these are easier to implement. We can create one, when we want a single variable to hold multiple types of related data. In visual basic 2005, we can one using 'Structure-and-End-Structure' statements. The members are declared in between the 'Structure-and-End-Structure' statements. For example, we can maintain Stock details in a single variable, we can do it as follows:

Structurestock_details
 Public Inv_No as String
 Public Inv_Date as Date
 Public ItemName as String
 Public Qty as Integer
End Structure


The variables declared are called data members. The access modifiers that we can use and the Access Scope defined by each access modifier are listed below.
  1. Public
  2. Declared with the Public keyword is accessible from anywhere within or outside the application. This is the default access mode.
  3. Friend
  4. Declared with the Friend keyword is accessible from within the program that contains its declaration and from anywhere else in the same program.
  5. Private
  6. Declared with the Private keyword is accessible only from within its declaration context, including any nested procedures.
  7. Protected
  8. Declared with the Protected keyword is accessible only from within its own class or from a derived class.
  9. Protected Friend
  10. Declared with the Protected Friend keyword is accessible from within the same assembly and in the derived classes.

We can also include procedures as members. For example, if you want to include a procedure to check the value entered for the stock variable, we can define it as shown below:

Structurestock_details 
Public Inv_No As String 
Public Inv_Date As Date 
Public ItemName As String 
Public Qty As Integer 

Public Sub CheckQty(BYVal Qty As Integer) 
If Qty < 10 Then 
  Qty=10  
End If 
End Sub
End Structure


Storing Data

After we declare, we can create the objects. The objects enables us to access the members by using the dot notation.

Dim inv1 As  stock_details
Inv1.Inv_No ="I001"
Inv1.Inv_Date=#5/31/2005# 
Inv1.ItemName ="ABC"
Inv1.Qty=1000

In the above example, inv1 is a type variable and Inv_No, Inv_Date, ItemName and Qty are the members of the type variable.

Accessing Data

You can access a member variable to validate the data stores in the members in the following manner:

If inv1.InvNo= " " Then
MsgBox ("Please enter the Invoice Number")
End If

Summary

In this article we have seen how to create, store data and access data from a structure.







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