Difference Between Classes And Structures
Oct 23, 2010
I know that Structures are value types and classes are reference type, i know that since structures are stored in stack they are faster to use i also understands that structures can not use the Inheritance concept but still in most examples i see i always see that the authors use classes when building something like BBL library, if structures is light-weight compare to classes and i don't need it to be inherited should i use structure instead of class?is there a rule of when to use class and when to use structure ?
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Feb 3, 2011
I've been programming a custom structure to use in my program for a while now and I am debating whether I should switch over to using a class instead. Reason being is because I've read from a few sources that structures should be kept for simple storage of primitive types. However, I am using my structure to store a few integers and a few custom classes of my own.I haven't noticed any slowdowns or performance issues but I do know that I have to update the actual variables in the structures since they are value types and not reference types.
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Dec 11, 2011
For the time being I have been using a Structure to store "people" (their name, gender, age, etc...), because I really love to refer to something like Mike.name or Caroline.age, so I could simply put Caroline.age += 1 anywhere in the code and here you go, Caroline is one year older. No more simpler.But because of how inflexible (compared to Classes) Structures appear to be, when I needed to iterate through all the instances I was forced to use a list or dictionary so I could use a FOR EACH ... NEXT block. That was resolved by you people in the previous post, but I'm having the problem that I couldn't use the elements of the list to change the original instance of the Structure proper... I mean, if I code something like this...
For Each thisperson As Person In peoplelist
If thisperson.name = person_selected Then
'person_selected is the SelectedItem.ToString of a listbox[code]....
Well, I thought that thisperson.teamleader and Mike.teamleader were going to be equivalent (when the IF statement was true, that is) but that doesn't appear to be the case. So right now I'm really hating Structures...But when I look into Classes... well, they have more flexibility, yes. You could construct a FOR EACH block without any other trick like the "on-top" list, and that it's very useful indeed, but (a big "but" IMHO) I lose that NICE feature that makes possible to write the name of one of them instances like Mike.age or Caroline. kills
I mean, if I wanted to add a year to Mike, well... there is no "Mike" in the first place. A "Mike" string could be a property for the class, but I cannot (or know) magically refer to him with the ease of a Structure, so when I want something so simple as Mike.age +=1 ...well, with a Class I'm simply clueless to how locate him and change ANOTHER property of him.I suppose I am doing something very wrong, because I cannot believe VBasic could force on you those two extreme philosophies...:
Classes = +flexibility -usability ???
Structures = -flexibility +usability ???
What I want to do is SO simple that I cannot believe I need to choose between the two.
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Aug 21, 2010
I've heard bad things about overusing regions but when adding enums to my classes I put them into a #region "Enums" at the end of the class, and do the same with structures and even subclasses.
Is there a better/standard way to go about grouping such elements on classes?
(Note: this is tagged C#/VB but maybe the same situation exists for other languages, like Java)
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Sep 27, 2009
I have tried this question several times, sometimes a little in the face of MS VB teams but with no constructive answers. Perhaps with too much rant. I suspect that VB.NET does not allow me to do what I can easly do in VB5.0. The VB team should easily be able to supply the information I need, but have not yet answered the questions. I want to do a lot of work on very large bitmaps (20 Mp or more; 80Mb or more ARGB) using arrays for access. This I used to do in VB5.0 using the SAFEARRAY and BITMAP STRUCTURES. NOT the corresponding .NET CLASSES. But I now need to use an SDK requiring .NET. However, through lack of wisdom, the VB team dropped 5 critical resources on the move to VB.NET - VarPtr, VarPtrArray, the 2 structures and CopyMemory. The SAFEARRAY CLASS seems to lack a set method for array data and the BITMAP CLASS seems to lack both get and set methods for data. On building a .NET solution using VB.NET, c#.NET and C++.NET projects I could not locate the set and get methods. Interop could not upgrade my VB5.0 to VB2005 - presumably on account of these 5 problems. I was surprised that even C++ suffered too. .NET hurts. So, first off, two critcal simple questions: A) Bearing in mind that much of the .NET is tinsel-wrapped APIs, does a pointer to an array still point to a defining SAFEARRAY STRUCTURE of the original format (NOT of course to a first element of an array). If that is so, I am lucky for I can then fill and use (perhaps) my own SAFEARRAY STRUCTURE by memory manipulation in C++. B) If the same applies to a bitmap pointer I can then perhaps do the same with BITMAP STRUCTURES. If that can be done I can hopefully work in a .NET solution containing C++ (for the pointer and mmory work) and VB2005 (for the rest of the work). I can then 1) in VB define two empty byte-arrays GLOBAL in VB.NET- Pic1() and Pic2(). They do not need to be dimensioned. SAFE FROM GC 2) in VB define two GLOBAL SAFEARRAYS to match the arrays, one with one and another with 2 dims matching the bitmap in size. SAFE FROM GC 3) move ByRef the 4 objects to VC++. STILL SAFE FROM GC, LEFT EXACTLY WHERE THEY WERE. 3) copy the BITMAP data pointers to the data pointers of the SAFEARRAYS. DOES NOT MOVE ANYTHING. 4) copy the addresses of the SAFEARRAYS to the corresponding arrays STILL DOES NOT MOVE ANYTHING, BUT JOB DONE. And then I will be able to process the images in seconds rather than minutes after moving only 4 4-byte numbers. I would welcome alternative sequences, provided they DO NOT involve put and set pixels or array elements on the trivial side and do not involve moving 80Mb of image data between "safe" and "unsafe" memory on the Herculian side. Else, as the Pic() ans Safearrays MUST point somehow to structures, WHAT EXACTLY ARE THEY, AND WHERE? I want to access them. If I can't overcome these 5 silly MS blunders I'll just have to build two uncoupled projects - one in VB5.0 and the other in VB/VC++ .NET. I'm not going to get involved myself with tinsel and gladwrap workarounds.
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Sep 1, 2011
I have been out of VB.Net way too long, I have a custom class in C# that needs to be converted to VB.Net and would like to know the main differences between them. Certain things in C# I cannot seem to do in Vb.Net with classes such as use: public classname or public [classname](DataTable dt) in VB.net
M[Code]...
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May 1, 2009
what is the difference between these 2 ways to refresh a linq class
1) LinqDB.Refresh
2) LinqDB =
New DataClasses1DataContext
I have got the impression that some time the linqdb.refresh does not work at all
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Jun 26, 2010
I want to know what are classes , objects , a namespace , subroutines,functions,methods,properties and differemce betweem byval and byref in your words.
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Jan 20, 2009
I have a structure called 'Scheme' and in my program I want (ideally) an ArrayList of 'Schemes' (so i can add, remove schemes etc.). However, within the 'Scheme' structure, I want to have an ArrayList of 'Item''Item' is another structure. Are there any solutions out there for iterating through these arrays quite easily?
How can I easily add multiple Items to a Scheme and mutliple Schemes to my Scheme array. Code is below. When I try to add Items to a Scheme, I get the 'Object not set to a reference of an object, try the 'New' keyword', but you cannot declare 'New' keywork within a structure.
[Code]...
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Jun 2, 2010
I read in the Book "Mastering Microsoft Visual Basic 2008" about "User-Defined data types".The example given is creating a Structure as follows.I wanted to check that so I wrote all the code given; I used a TextBox and a Button for this.(I didn't include the "CheckDate" here; that is in the book)
Structure CheckRecord
Dim CheckNumber As Integer
[code]....
The problem is this does work.What I get is "00000". and I found out that the "Checks(4)" Array does hold any value ie: on keeping the cursor over that, it shows "CheckAmount 0.0, CheckNumber 0 , CheckPaidTo Nothing ".
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Jan 23, 2012
I have two classes, one nested in the other. [code]Neither "Name" or "ID" are unique between operations and records.I wish to construct a dictionary using LINQ = Dictionary(Of String, Of List(Of Integer), whereby the keys are uniqe examples of Names in my collection and the values are the collective set of distinct IDs that are associated with those names.
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Jun 13, 2012
How can I structure my classes so that the user interfaces though a single class while the supporting classes are hidden from their view? I think its best understood in an example:
Public Class MyInterface
Public Economic as EconomicClass
Public Sub New()
MyBase.New()
[code].....
So you might ask why am I even separating them? It's strictly for others who will be working with this interface. I need to funnel them though a logical structure:
interface.Economic.MyMethod
interface.Currency.MyMethod
etc
This way everything is already handled for them in the background and they only need to run the method they need. I don't know if I can have it both ways in VB.NET.
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Oct 24, 2009
Here is some example code of what I mean:
vb
Public Class Form1
Private Sub Button1_Click(ByVal sender as Object, e as systemEventArgs) Handles Button1.Click
[Code]....
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Jul 20, 2009
I'm attempting to create a list of structures that contains a list of structures. I can't seem to figure out how to properly allocate the object for the inner list of structures. I expect the outer list of structures to have a couple thousand entries and the inner list of structures to be fairly small at 2 to 10. Both lists will grow over time but the number of elements within the inner list will be constant for an instance of the outer list. Meaning, if an instance of the outer list has 2000 entries each of those will have the same number of elements on the inner list, say 4 entries.
Here is a simplified code fragment. This fragment makes no attempt to create the instance of the inner list "StructBlist" since I can't figure out where to put it. Tried "New List(Of StructB)" in the declaration as well as "Alist(0).StructBlist = New List(Of StructB)" but neither works.
Public Class Form1
Structure StructA
Dim FieldA1 As Integer
[Code]....
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Jul 10, 2009
I m trying to raise Click event of Textbox explictly but I m getting "Derived classes cannot raise base classes" error.[code]....
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Sep 24, 2010
so far i got
code
For Each item As Reflection.FieldInfo In GetType(NameSpace.ClassWithNestedClasses).GetFields
rtfAppend(item.Name & ":" & Tab & item.GetValue(Me))
Next
For Each item As Reflection.PropertyInfo In GetType(NameSpace.ClassWithNestedClasses).GetProperties()
[code]...
which gets me the simple string vars and properties of my top class, but how can i apply this to loop through all sub classes and get there vars and props?
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Oct 13, 2011
Searching the internet finds no less than 700 different ways and opinions to accomplish what I'm trying to do, and I would just like to know the simplest, most bullet-proof way possible.
[Code]...
I simply want to extract the string "bar," which is inside <hostName></hostName>I can do this easily enough with simple string functions, but I'd like to do it with one of the .NET XML classes/methods.
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Mar 28, 2010
What is the different between these 2 structures?
Structure INPUT
Public dwType As InputType
Public mi As MOUSEINPUT
Public ki As KEYBDINPUT
End Structure
[Code]...
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May 14, 2011
Structure TextureStruct
Dim unk1 As ULong 'always 0x70007
Dim unk2 As ULong 'always 0x70007
Dim unk3 As ULong 'always 0x70007
Dim unk4 As ULong 'always 0x70007
Dim unk5 As ULong 'always 0x70007
Dim unk6 As ULong 'always 0x70007
[Code]...
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Jun 5, 2010
Is it possible to declare a new list inside a structure.
I'm trying to get a list of structures that each contain a list of points,
but when i try to declare a new list inside the structure VB says "keyword not valid as an identifier"
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May 24, 2009
I'm currently doing this project where i have to create a program that let's the administrator manage students (and their tests.) I have decided to use Random Access file in this project.because structures will need fixed lengths...i don't know how will i search through the students (a function of the program) when each student structure has a different length because of the number of tests they've done.* I have created a variable in the aStudent structure so that i can know the number of tests a student has done...but don't know how to use it.
Public Class FormAdmin
Dim currentStudentName As String
Dim currentStudentID As Integer = 0
[code]....
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Jun 18, 2011
I have created a structure as below. I want the structure to be an array...so I can use a call like picks(1).a or picks.a(1) = blah blah. I don't understand how to use an array of a structure..
Public Structure apicks
Dim a As String
Dim b As String
End Structure
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Mar 8, 2010
I have been trying to read the cd toc in one go from the API, I can read it OK with a single byte array, but I can't find a way to fill the formatted arrays
Code:
'ORIGINAL STRUCTS
'MAXIMUM_NUMBER_TRACKS = 99
'typedef struct _CDROM_TOC {
' UCHAR Length[2];
[code].....
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May 22, 2011
what is the best way to add, delete elements from arrays of structures structure
vb
Structure Proxy
Dim Server As String
[Code].....
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Jan 21, 2010
I am currently working on a project for myself which looks through employee's information to find their availability to work. I've tried making a structure which holds the employee's information but I can't think of a good way to create different instances of it and store information in it at runtime. I'd prefer to load the information in at startup and not have to declare each employee and information. I am very new to Visual Basic 2008 but I have a good grasp of arrays from C and C++.
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May 1, 2012
lets say its something like[code]...
i want to add a function like this inside the structure
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Nov 7, 2009
I have a Structure, and I am having trouble initialising it. Specifically when I try to populate the Vector3 variables, it tells me that they are Nothing, so I need to make them New when the array of this structure is declared.[code]Structures cannot declare a non-shared 'Sub New' with no parameters.I have no parameter to supply, and this will be an array so I'm not even sure how I would supply it.The second option to fix the error is to make the Sub New shared, but then I get other errors: Cannot refer to an instance member of a class from within a shared method or shared member initializer without an explicit instance of the class.Does anyone know how I can resolve this. My end goal is to have an array of this structure type with the Vector3s ready to use.
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Mar 10, 2009
I have created a collection of structures. Each structure, of course, contains fields.
Lets say something like:
Public Structure clientStructure
Public ID As String
Public firstName As String
[Code]....
How can I access a field of a particular structure using for.... each?
That is, how can I retrieve out of the collection (lets say item 5's) firstName, using for...each?
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Sep 1, 2009
Can a list class in vb.net contain Data Structures ?
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Jul 26, 2009
Just a little frustrated with a simple error in a listbox result on a mobile application.Here is a sample of the results I should be getting:
The inputs are 50mph & 4.5 hours
Hour distance
1 50
[code].....
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