class lock Property public, private static

Global variable

A global variable can be useful, but it may lead to problems that are hard to debug. Global variables can cause errors in software development.

Many programs can benefit from global variables if used in a controlled manner. We use the static keyword. A separate static class can also be used.

Example

The static keyword describes something that is part of a type, not an instance of the type. This word was chosen for historical reasons—it was used in C and C++.

Here We see the GlobalVar class, which contains the global variables in a static class, and Program, which uses the global class.

Note GlobalString is a public global variable. You must assign its value inline with its declaration at the class declaration space.

Note 2 GlobalValue is a public static property with get and set accessors. This is an access routine of a backing store.

Warning A global field could cause problems in your program because it does not use an access routine.

using System;

/// <summary>
/// Contains global variables for project.
/// </summary>
public static class GlobalVar
{
    /// <summary>
    /// Global variable that is constant.
    /// </summary>
    public const string GlobalString = "Important Text";

    /// <summary>
    /// Static value protected by access routine.
    /// </summary>
    static int _globalValue;

    /// <summary>
    /// Access routine for global variable.
    /// </summary>
    public static int GlobalValue
    {
        get
        {
            return _globalValue;
        }
        set
        {
            _globalValue = value;
        }
    }

    /// <summary>
    /// Global static field.
    /// </summary>
    public static bool GlobalBoolean;
}

class Program
{
    static void Main()
    {
        // Write global constant string.
        Console.WriteLine(GlobalVar.GlobalString);

        // Set global integer.
        GlobalVar.GlobalValue = 400;

        // Set global boolean.
        GlobalVar.GlobalBoolean = true;

        // Write the 2 previous values.
        Console.WriteLine(GlobalVar.GlobalValue);
        Console.WriteLine(GlobalVar.GlobalBoolean);
    }
}Important Text
400
True

Access routines

Global variables are used most effectively when accessed through special methods called access routines. You can use access routines in nearly any programming language.

Tip These methods provide another layer of abstraction over how you use the global variables.

Threads

Static fields can introduce problems when using multithreading, which is used extensively in websites. An access routine could provide locking using the lock-statement.

Also This is a problem in many Windows Forms applications that use BackgroundWorker threads.

Summary

We used global variables by adding a static class with constants, properties and public fields. You can also define methods with parameters to access the static variables.