working of static main methos.

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Hi , please help me understanding this situation...

class Program
{
    int i;
    static void Main(string[] args)
    {
        cl obj = new cl();
      //  i=34;   <-- cant access since it is not static.
    }}

class cl
{
public  void display()
{}}

My problen is that in the void main method (which does not allows non-static members in it, how come am i able to create an instance of the 'cl' class (which is non-static)???
Why does it NOT give an error :
"An object reference is required for the non-static field, method, or property."

[edit]Code block added - OriginalGriff[/edit]

Posted 2-Jul-11 1:17am

shikhar gilhotra

Updated 2-Jul-11 1:41am

OriginalGriff

v2

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OriginalGriff · Answer 1 · 2011-07-02T01:38:00

Simple: The Main method is always static - there is only ever one of these (or the framework wouldn't know which instance to run on startup), so it runs fine. But, it is static, which means it is not attached to any instance, and so has no this pointer, either implied or specified. As a result, you cannot use "i" because it is not a static property, and requires a specific instance to give you the this pointer.

When you do this:

cl obj = new cl();

you create an instance of the "cl" class, referred to by a variable within Main, called "obj". Because it is an instance, it can have all the properties it needs, and it persisted until it goes out of scope - in this case by the code reaching the end of the Main method.

If you couldn't do this, you could never instantiate any class, and your program would have to be very short, and boring!

De, Subhendu · Answer 2 · 2011-07-02T07:53:00

Solution 2

class Program
{
    static void Main(string[] args)
    {
        cl.display();
    }
}
class cl
{
    public static void display() {}
}

Posted 2-Jul-11 7:53am

De, Subhendu

Comments

Sergey Alexandrovich Kryukov 2-Jul-11 20:00pm

My 4. You still don't show how to call instance methods.
There is much more convenient pattern, please see my answer.
--SA

Sergey Alexandrovich Kryukov · Answer 3 · 2011-07-02T13:59:00

First, you need to understand static and non-static members. Non-static method is called instance method. It can be called only on instance, not the class like static and is given access to a concrete instance of the class or structure as it appears during run-time call. How? It simply has a hidden parameter of the class/structure type passed during actual call. This parameter is called "this" and can be used explicitly, such as this.MyField.

Now, the function Program.Main is static (this is the only way to make an entry point; how else if there are no any instances yet?), the class Program does not have to be static (but it can).

So, I can suggest you a simple pattern:

C#

class Program {

   void Run() { //instance method, not a static one
       //access any instant or static members here
   }

   static void Main(string[] args) {
       new Program().Run(); //here you go from static to instance way
   }

}

—SA

working of static main methos.

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