static (C# Reference)
This page covers the static modifier keyword. The static keyword is also part of the using static directive.
Use the static modifier to declare a static member, which belongs to the type itself rather than to a specific object. The static modifier can be used to declare static classes. In classes, interfaces, and structs, you may add the static modifier to fields, methods, properties, operators, events, and constructors. The static modifier can't be used with indexers or finalizers. For more information, see Static Classes and Static Class Members.
You can add the static modifier to a local function. A static local function can't capture local variables or instance state.
You can add the static modifier to a lambda expression or anonymous method. A static lambda or anonymous method can't capture local variables or instance state.
Example - static class
The following class is declared as static and contains only static methods:
static class CompanyEmployee
{
public static void DoSomething() { /*...*/ }
public static void DoSomethingElse() { /*...*/ }
}
A constant or type declaration is implicitly a static member. A static member can't be referenced through an instance. Instead, it's referenced through the type name. For example, consider the following class:
public class MyBaseC
{
public struct MyStruct
{
public static int x = 100;
}
}
To refer to the static member x, use the fully qualified name, MyBaseC.MyStruct.x, unless the member is accessible from the same scope:
Console.WriteLine(MyBaseC.MyStruct.x);
While an instance of a class contains a separate copy of all instance fields of the class, there's only one copy of each static field.
It isn't possible to use this to reference static methods or property accessors.
If the static keyword is applied to a class, all the members of the class must be static.
Classes, interfaces, and static classes may have static constructors. A static constructor is called at some point between when the program starts and the class is instantiated.
Note
The static keyword has more limited uses than in C++. To compare with the C++ keyword, see Storage classes (C++).
To demonstrate static members, consider a class that represents a company employee. Assume that the class contains a method to count employees and a field to store the number of employees. Both the method and the field don't belong to any one employee instance. Instead, they belong to the class of employees as a whole. They should be declared as static members of the class.
Example - static field and method
This example reads the name and ID of a new employee, increments the employee counter by one, and displays the information for the new employee and the new number of employees. This program reads the current number of employees from the keyboard.
public class Employee4
{
public string id;
public string name;
public Employee4()
{
}
public Employee4(string name, string id)
{
this.name = name;
this.id = id;
}
public static int employeeCounter;
public static int AddEmployee()
{
return ++employeeCounter;
}
}
class MainClass : Employee4
{
static void Main()
{
Console.Write("Enter the employee's name: ");
string name = Console.ReadLine();
Console.Write("Enter the employee's ID: ");
string id = Console.ReadLine();
// Create and configure the employee object.
Employee4 e = new Employee4(name, id);
Console.Write("Enter the current number of employees: ");
string n = Console.ReadLine();
Employee4.employeeCounter = Int32.Parse(n);
Employee4.AddEmployee();
// Display the new information.
Console.WriteLine($"Name: {e.name}");
Console.WriteLine($"ID: {e.id}");
Console.WriteLine($"New Number of Employees: {Employee4.employeeCounter}");
}
}
/*
Input:
Matthias Berndt
AF643G
15
*
Sample Output:
Enter the employee's name: Matthias Berndt
Enter the employee's ID: AF643G
Enter the current number of employees: 15
Name: Matthias Berndt
ID: AF643G
New Number of Employees: 16
*/
Example - static initialization
This example shows that you can initialize a static field by using another static field that is not yet declared. The results will be undefined until you explicitly assign a value to the static field.
class Test
{
static int x = y;
static int y = 5;
static void Main()
{
Console.WriteLine(Test.x);
Console.WriteLine(Test.y);
Test.x = 99;
Console.WriteLine(Test.x);
}
}
/*
Output:
0
5
99
*/
C# language specification
For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.
