Differences between struct and classes are:
|Struct are value types; A variable of a structure type contains the structure’s data.
|Classes are reference types. A variable of a class type contains a reference to the data as a class type does.
|Struct use stack allocation.
|Classes use heap allocation.
|All struct elements are Public by default.
|A class variables and constants are Private by default, while other class members are Public by default.
|A struct must have at least one nonshared variable or nonshared, noncustom event element.
|A class can be completely empty.
|Struct elements cannot be declared as Protected.
|A class members can declare as element as Protected.
|Struct variable declarations cannot specify initializers or initial sizes for arrays;
|class variable declarations can specify initializers or initial sizes for arrays;
|Struct implicitly inherit from the System.ValueType class and cannot inherit from any other type.
|Classes can inherit from any class or classes other than System.ValueType
|Struct are not inheritable
|classes are inheritable
|Struct are never terminated, so the common language runtime (CLR) never calls the Finalize method on any structure
|classes are terminated by the garbage collector (GC), which calls Finalize on a class when it detects there are no active references remaining
|A struct does not require a constructor
|a class does need a constructor
|Struct can have nonshared constructors only if they take parameters.
|Classes can have them with or without parameters.
|A struct procedure can handle events only if it is a static method, and only by means of the AddHandler Statement
|Any class procedure can handle events, using either the Handles keyword or the AddHandler statement.
Every struct has an implicit public constructor without parameters. This constructor initializes all the struct’s data elements to their default values. You cannot redefine this behaviour
Instances and Variables: Because structs are value types, each struct variable is permanently bound to an individual struct instance. But classes are reference types, and an object variable can refer to various class instances at different times.
This distinction affects your usage of struct and classes in the following ways:
A struct variable implicitly includes an initialization of the elements using the struct’s parameterless constructor. Therefore,
struct s ; is equivalent to struct s1 = new struct() ;
- Assigning Variables.
When you assign one struct variable to another, or pass a structure instance to a procedure argument, the current values of all the variable elements are copied to the new structure. When you assign one object variable to another, or pass an object variable to a procedure, only the reference pointer is copied.
- Assigning Null.
You can assign the value “null” to a struct variable, but the instance continues to be associated with the variable. You can still call its methods and access its data elements, although variable elements are reinitialized by the assignment.
In contrast, if you set an object variable to “null “, you dissociate it from any class instance, and you cannot access any members through the variable until you assign another instance to it.
- Multiple Instances.
An object variable can have different class instances assigned to it at different times, and several object variables can refer to the same class instance at the same time. Changes you make to the values of class members affect those members when accessed through another variable pointing to the same instance.
Struct elements, however, are isolated within their own instance. Changes to their values are not reflected in any other structure variables, even in other instances of the same Struct declaration.
Equality testing of two struct must be performed with an element-by-element test.
Two object variables can be compared using the Equals method. Equals indicates whether the two variables point to the same instance.