The struct (structure) is like a class in C# that is used to store data. However, unlike classes, a struct is a value type.
Suppose we want to store the name and age of a person. We can create two variables: name and age and store value.
However, suppose we want to store the same information of multiple people.
In this case, creating variables for an individual person might be a tedious task. To overcome this we can create a struct that stores name and age. Now, this struct can be used for every person.
Define struct in C#
In C#, we use the struct keyword to define a struct. For example,
struct Employee {
public int id;
}
Here, id is a field inside the struct. A struct can include methods, indexers, etc as well.
Declare struct variable
Before we use a struct, we first need to create a struct variable. We use a struct name with a variable to declare a struct variable. For example,
struct Employee {
public int id;
}
...
// declare emp of struct Employee
Employee emp;
In the above example, we have created a struct named Employee. Here, we have declared a variable emp of the struct Employee.
Access C# struct
We use the struct variable along with the . operator to access members of a struct. For example,
struct Employee {
public int id;
}
...
// declare emp of struct Employee
Employee emp;
// access member of struct
emp.id = 1;
Here, we have used variable emp of a struct Employee with . operator to access members of the Employee.
emp.id = 1;
This accesses the id field of struct Employee.
Note: Primitive data types like int, bool, float are pre-defined structs in C#.
Example: C# Struct
using System;
namespace CsharpStruct {
// defining struct
struct Employee {
public int id;
public void getId(int id) {
Console.WriteLine("Employee Id: " + id);
}
}
class Program {
static void Main(string[] args) {
// declare emp of struct Employee
Employee emp;
// accesses and sets struct field
emp.id = 1;
// accesses struct methods
emp.getId(emp.id);
Console.ReadLine();
}
}
}
Output
Employee Id: 1
In the above program, we have created a struct named Employee. It contains a field id and a method getId().
Inside the Program class, we have declared a variable emp of struct Employee. We then used the emp variable to access fields and methods of the class.
Note: We can also instantiate a struct using the new keyword. For example,
Employee emp = new Employee();
Here, this line calls the parameterless constructor of the struct and initializes all the members with default values.
Constructors in C# struct
In C#, a struct can also include constructors. For example,
struct Employee {
public int id;
// constructor
public Employee(int employeeId) {
id = employeeId
}
}
Here, we have created a parameterized constructor Employee() with parameter employeeId.
Note: We cannot create parameterless constructors in C# version 9.0 or below.
Example: Constructor in C# structs
using System;
namespace CsharpStruct {
// defining struct
struct Employee {
public int id;
public string name;
// parameterized constructor
public Employee(int employeeId, string employeeName) {
id = employeeId;
name = employeeName;
}
}
class Program {
static void Main(string[] args) {
// calls constructor of struct
Employee emp = new Employee(1, "Brian");
Console.WriteLine("Employee Name: " + emp.name);
Console.WriteLine("Employee Id: " + emp.id);
Console.ReadLine();
}
}
}
Output
Employee Name: Brian Employee Id: 1
In the above example, we have created a parameterized constructor inside the Employee struct. Inside the constructor, we have assigned the values of fields: id and name.
Notice the line,
Employee emp = new Employee(1, "Brian");
Like in C# classes, we are using the new keyword to call the constructor. Here, 1 and "Brian" are arguments passed to the constructor, where they are assigned to the parameters employeeID and employeeName respectively."
Note: We must assign the value for every field of struct inside the parameterized constructor. For example,
// error code
public Employee(int employeeID, employeeName) {
id = employeeID;
}
Here, we have not assigned the value for the name field. So the code will generate an error.
Properties in C# struct
We can also use properties inside a C# struct. For example,
using System;
namespace CsharpStruct {
// defining struct
struct Employee {
public int id;
// creates property
public int Id {
// returns id field
get {
return id;
}
// sets id field
set {
id = value;
}
}
}
class Program {
static void Main(string[] args) {
// calls the constructor of struct
Employee emp = new Employee();
emp.Id = 1;
Console.WriteLine("Employee Id: " + emp.Id);
Console.ReadLine();
}
}
}
Output
Employee Id: 1
In the above example, we have Id property inside the Employee struct.
The get method returns the id field and the set method assigns the value to the id field.
Difference between class and struct in C#
In C# classes and structs look similar. However, there are some differences between them.
A class is a reference type whereas a struct is a value type. For example,
using System;
namespace CsharpStruct {
// defining class
class Employee {
public string name;
}
class Program {
static void Main(string[] args) {
Employee emp1 = new Employee();
emp1.name = "John";
// assign emp1 to emp2
Employee emp2 = emp1;
emp2.name = "Ed";
Console.WriteLine("Employee1 name: " + emp1.name);
Console.ReadLine();
}
}
}
Output
Employee1 name: Ed
In the above example, we have assigned the value of emp1 to emp2. The emp2 object refers to the same object as emp1. So, an update in emp2 updates the value of emp1 automatically.
This is why a class is a reference type.
Contrary to classes, when we assign one struct variable to another, the value of the struct gets copied to the assigned variable. So updating one struct variable doesn't affect the other. For example,
using System;
namespace CsharpStruct {
// defining struct
struct Employee {
public string name;
}
class Program {
static void Main(string[] args) {
Employee emp1 = new Employee();
emp1.name = "John";
// assign emp1 to emp2
Employee emp2 = emp1;
emp2.name = "Ed";
Console.WriteLine("Employee1 name: " + emp1.name);
Console.ReadLine();
}
}
}
Output
Employee1 name: John
When we assign the value of emp1 to emp2, a new value emp2 is created. Here, the value of emp1 is copied to emp2. So, change in emp2 does not affect emp1.
This is why struct is a value type.
Moreover, inheritance is not possible in the structs whereas it is an important feature of the C# classes.