static vs Instance constructors

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Hello,

I experimented with a code:

C#

class gen<t>
   {
       static int count = 0;
       static gen()
       {
           Console.WriteLine("created: {0}",count.ToString());
           count++;
       }

   }

C#

class Program
   {
       static void Main(string[] args)
       {

           gen<string> g1 = new gen<string>();
           gen<int> g2 = new gen<int>();
           gen<guid> g3 = new gen<guid>();



           gen<string> g11 = new gen<string>();
           gen<int> g22 = new gen<int>();
           gen<guid> g33 = new gen<guid>();




           Console.ReadLine();

       }
   }

- It prints:

created: 0<br />
  created: 0<br />
  created: 0

- It prints this once for each type. If i use an instance constructor then the output would be:

created: 0<br />
  created: 0<br />
  created: 0<br />
  created: 1<br />
  created: 1<br />
  created: 1<br />

- This means that an instance constructor gets initialized every time. Now my doubt is that if use a static constructor then the object is created just once on the heap as against an instance constructor?
- The next thing is: whats better to use: static or an instance constructor.
- Because by using an instance constructor i can pass arguments multiple times depending upon the scenario: which means that i can produce a variety of result sets. Am i correct?
- When to use an instance constructor and when to use a static constructor?

Thanks and regards,
-Rahul

Posted 6-Jan-14 20:28pm

Rahul VB

Updated 6-Jan-14 20:30pm

uspatel

v2

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3 solutions

Solution 3

MSDN wrote:
A static constructor is used to initialize any static data, or to perform a particular action that needs to be performed once only. It is called automatically before the first instance is created or any static members are referenced.

Posted 6-Jan-14 21:43pm

Maciej Los

Updated 6-Jan-14 22:01pm

v2

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uspatel · Accepted Answer · 2014-01-06T20:49:00

Solution 1

As Static constructor called first time as class is referenced

C#

TestClass.MyStaticMethod()

So you need to create a static constructor when you want to initialize any static data, or to perform a particular action that needs to be performed once only.
and
use Instance constructor whenever you want to to create and initialize any instance member variables that you use the new expression to create an object of a class.

Posted 6-Jan-14 20:49pm

uspatel

Comments

Rahul VB 7-Jan-14 5:53am

Sir,
Thanks. This means that i can create a new variety of results using an instance constructor. And static constructor, fields, methods are initialized just once(I hope i have understood correctly).
That means :
Class()
{
static method1();
}

so if i say:
Class.Method1(); //then this would work just once?
then what would happen if i say :
Class.Method1() ;
Class.Method1() ;
Class.Method1() ;
/// then the output would be just once? as i am using a static method? Please correct me if i am wrong.

Thanks,
- Rahul

uspatel 7-Jan-14 7:15am

static method are called by classed name.as you code,these method called three times.
But here we are discussing static constructor
public class SS
{
static readonly long baseline;
static SS()
{
baseline = DateTime.Now.Ticks;
}
public static void Method(int a)
{

Console.WriteLine(a);
Console.WriteLine(baseline);
}

}
Now call as
public static void Main()
{

SS.Method(10);
SS.Method(20);
SS.Method(30);
Console.ReadKey();
}
See example here value of baseline will be same as it is static.

10
635247135133415819
20
635247135133415819
30
635247135133415819

Rahul VB 7-Jan-14 7:22am

Sir,
Ok now i get it, so a static constructor is initialized once.
Thanks,
-Rahul

Raul Iloc · Accepted Answer · 2014-01-06T20:53:00

1.In generally a static constructor is used to initialize the static members of a class and it is invoked first time before to create a new object of that type OR before to invoke any of its static members. So the static constructor cannot be invoked manually and they are automatically invoked by the .NET before to access any member and methods of the class (including the non static constructors)!!!

2.In your example you are using templates and is more complicated, but the principle is the same: when you invoke an instance constructor for a given "template type", then ONLY if is the first time when that "template type" is used, before you instance constructor code to be executed, the static constructor is executed like the 1st rule above said.

PS: To understand better the static constructors I recommend you first to test them for normal classes (that are not using templates), then to complicate the problem like in your example by using templates.