I know in VB you can define a UDT like:
Public Type Buffer1
ProductCode As String
SerialNumber As String
Date As Date
End Type
Is it possible to create a User Defined Type in C#? I know that they are used to implement data structures. I have researched and cannot seem to find anything.
The .NET equivalent of the VB6 Type is a struct with public fields. If what you need is the equivalent of the VB6 type, you should the ignore people who are telling you not to use a mutable struct.
Some people believe all data types should behave like class objects, and since structs with exposed fields behave in ways that class objects cannot they are evil.
In reality, there are times when the equivalent of a VB6 Type can be very useful, and any attempt to achieve such functionality with anything other than an exposed-field or otherwise "mutable" struct will be more cumbersome and yield less performant code than would using a type whose natural semantics precisely match what one is trying to achieve. Note that struct fields should generally be exposed as fields rather than properties, since the whole purpose of a VB6 Type is to serve as an aggregation of data types, rather than an ecapsulation of protected state.
There is, alas, one problem with .NET structure types, which is that unless you declare a structure as an unsafe type, only usable within unsafe code (and not usable in contexts which require being able to run in a Partial Trust environment), arrays within structures cannot achieve the semantics of arrays nor fixed-length strings in a VB6 Type. C# will allow one to declare fixed-sized arrays within a struct using the fixed keyword, but as noted only in conjunction with unsafe. Any other array declarations within a struct will cause a struct to hold an array reference rather than an array. Thus:
struct MyStruct {int n; int[] Arr; }
MyStruct a,b;
a.Arr = new int[4];
a.Arr[0] = 3;
a.n = 1;
b=a; // Copies the value of n, and the array reference in Arr, but not the array contents
b.n = 2;
b.Arr[1] = 2;
After the above code runs, b has its own copy of variable n, so the write to b.n will not affect a.n. Field b.Arr, however, holds a reference to the same array as a.Arr. An assignment directly to field Arr of b could make it point to a different array from a.Arr, but the assignment to b.Arr[1] doesn't actually write to field Arr but instead writes to the array object identified by that field, which is the same object identified by field a.Arr.
In some cases, you can replace what in VB6 would be a fixed-sized array with a simple list of discrete variables. Icky, but workable. Alternatively, if the restrictions associated with fixed arrays aren't a problem, you could use those. Beyond that, there isn't any good way to include arrays within a structure.
A "User Defined Data Type" from Visual Basic is called a Structure in VB.Net, and a struct in C#.
public struct Buffer1
{
public string ProductCode;
public string SerialNumber;
public DateTime Date;
}
Note that unlike the VB6 Type, which always makes all fields public, fields in all .NET types, including structures, default to private.
C# have classes and structs:
public class Buffer1
{
string ProductCode;
string SerialNumber;
DateTime Date;
}
But if you don't know classes, you must previously read some articles or books about C# (e.g. CLR via C#)
