In C#, structures are value type data structures. You can use them to encapsulate small amounts of related data. A structure includes a number of data member declarations which are called its fields, and methods.
Here is an example of how to define a structure:
public struct Book
{
public string title;
public string author;
public string subject;
public int book_id;
}
In this example, `Book` is a structure that includes four fields: `title`, `author`, `subject`, and `book_id`.
You can create an instance of a structure in the following way:
Book book1;
book1.title = "Programming in C#";
book1.author = "John Doe";
book1.subject = "Programming";
book1.book_id = 12345;
Or you can initialize the structure at the time of declaration:
Book book2 = new Book { title = "Data Structures", author = "Jane Doe", subject = "Computer Science", book_id = 67890 };
Key Characteristics of Structures in C#:
1. Value type: Structures are value types. When a structure is assigned to a new variable, the new variable gets a copy of the original values. So, changes made to one variable don't affect the other variable.
2. Inheritance: Structures don't support inheritance, and hence cannot be extended (though they can implement interfaces).
3. Default Constructor: A structure has a default constructor and cannot have a custom parameterless constructor.
4. Instantiation: When you instantiate a struct object using the new operator, it gets created and the appropriate constructor is called. Unlike classes, structs can be instantiated without the new operator.
5. Memory Allocation: When a struct is created, the memory is allocated on the stack.
Access Specifiers:
Access specifiers, also known as access modifiers, determine the visibility of a structure and its members. There are four types of commonly used access specifiers in C#:
1. Public: The public keyword is an access modifier for types and type members. Public access is the most permissive access level. There are no restrictions on accessing public members.
2. Private: The private keyword is a member access modifier. Private access is the least permissive access level. Private members are accessible only within the body of the class or the struct in which they are declared.
3. Protected: The protected keyword is a member access modifier. A protected member is accessible within its class and by derived class instances.
4. Internal: The internal keyword is an access modifier for types and type members. Internal types or members are accessible only within files in the same assembly.
In the context of structures in C#, remember that you can't declare the structure itself as private or protected, but the members of the structure (fields, properties, methods, etc.) can have these access modifiers. By default, if you do not specify an access modifier, it will be `private`.
public struct Book
{
public string title;
private string author;
protected string subject;
internal int book_id;
}
