CODEWITHSUNDEEP
c#classprogram-entry-point
Bluefire
Bluefire

Reputation: 14109

C# class without main method

I'm learning C# and I'm very new to it, so forgive me for the seemingly stupid question. I have some experience in Java, and I noticed that C# programs also need a main() method in their main class.

What if I want to create a class that isn't a main class, i.e. one that I import into a main class?

I tried to do that, and when I compile (via cmd using csc File.cs) the compiler says that the .exe that it will make has no main() method. Does that mean that I was wrong, and every class needs a main() method, or that I'm compiling it wrongly?

Maybe the problem's in the code (since I'm relying on my knowledge of Java syntax), which looks like this:

public class Class
{
    int stuff;
    public Class(int stuff)
    {
        this.stuff = stuff;
        stuff();
    }
    public void method()
    {
        stuff();
    }
}

EDIT: I'm afraid this is terribly misunderstood. I'm not asking if the file needs a main method, I'm asking how I can import this class into another class, because I realise that if I am to do this I can't have a main (as I said, I have some Java experience), but whenever I try to compile without one the compiler tells me that I need one.

Upvotes: 13

Views: 40591

Answers (10)

Parimal Raj
Parimal Raj

Reputation: 20575


##Not all classes need `Main` method.

As MSDN States

The Main method is the entry point of a C# console application or windows application. (Libraries and services do not require a Main method as an entry point.). When the application is started, the Main method is the first method that is invoked.

There can only be one entry point in a C# program. If you have more than one class that has a Main method, you must compile your program with the /main compiler option to specify which Main method to use as the entry point.

Only one class need to keep the Main method, the class which acts as entry point of the application.

The signature of the main method is : static void Main(string[] args) or static void Main() or static int Main(string[] args) or static int Main()

Check out this link for more details : Main() and Command-Line Arguments (C# Programming Guide)

For your above example:

public class MyClassName // changed the class name, avoid using the reserved keyword :P
{
    int stuff;
    public MyClassName(int stuff)  // is the constructor
    {
        this.stuff = stuff;
    }
    public void method()
    {
        stuff = 1;
    }
}

If you need to use that class, you can create a static class with main method:

class ProgramEntry
{
    static void Main(string[] args)
    {
        MyClassName classInstance = new MyClassName(2);
        classInstance.method();
    }
}

Starting C# 9 the option to have a program without the Main method has been introduced. Instead of having to declare the Main method, you can now write code directly in a file outside of a class. For more details see Top-level statements - programs without Main methods.

Upvotes: 28

Vivek Nuna
Vivek Nuna

Reputation: 1

Main is required, but C#9 has this feature such that you will not write Main but it will act as Main.

In C# 9.0 you can just choose to write your main program at the top level instead:

using System;

Console.WriteLine("Hello World!");

Any statement is allowed. The program has to occur after the usings and before any type or namespace declarations in the file, and you can only do this in one file, just as you can have only one Main method today.

If you want to return a status code you can do that. If you want to await things you can do that. And if you want to access command-line arguments, args is available as a “magic” parameter.

Local functions are a form of statement and are also allowed in the top-level program. It is an error to call them from anywhere outside of the top-level statement section.

Reference: https://devblogs.microsoft.com/dotnet/welcome-to-c-9-0/#top-level-programs

Upvotes: 0

Abdul Karim Siddiqui
Abdul Karim Siddiqui

Reputation: 11

C# class without Main() means, you can compile it as a library (.dll) csc /target:library YourClassFileName.cs or csc /t:library YourClassFileName.cs to make it as YourClassFileName.dll file and then you can use it in another class file which have the Main() method (Entry point)

csc /reference:YourClassFileName.cs YourMainClassFileName.cs or csc /r:YourClassFileName.cs YourMainClassFileName.cs

to make an YourMainClassFileName.exe file

Upvotes: 1

kittu
kittu

Reputation: 7008

Only one class with one method should be fine. If you want, you can set up the start up object in visual studio in the settings.

Upvotes: 1

Botz3000
Botz3000

Reputation: 39610

You only need a main method when you build an executable assembly (.exe), and you only need it in one class. This method will be the default entry point where execution starts. You don't need a main method when you build your code as a class library (.dll).

Upvotes: 1

Matt Burland
Matt Burland

Reputation: 45135

Try using /t:library switch with the compiler. By default it tries to make an .exe which, of course, needs an entry point (i.e. a main method). If you compile to a .dll you won't need that.

But as HighCore suggested, if you are learning, just use Visual Studio (download one of the free versions if you haven't already) and let it worry about the compiler flags.

Upvotes: 1

Robert
Robert

Reputation: 112

If this is a console application, you need a Main method to start with. Otherwise (web application, for example), you don't need one.

Upvotes: 1

Dialecticus
Dialecticus

Reputation: 16761

C# application must have at least one class with Main method, so that execution can begin from it. Application can have plenty of classes, but only one class with only one Main method is required.

C# library does not have to have a Main method.

Upvotes: 1

chue x
chue x

Reputation: 18803

In this scenario you need at least one class in your code with the Main method in it. The other classes do not need the Main method.

Upvotes: 1

Felipe Oriani
Felipe Oriani

Reputation: 38598

static void main(string[] args) method in C# programs is the start point to execute. If you try to compile a single C# File, the compiler will find this method to start the execution. You don't need to create the method in a class you are using as a model, but you have to have this method on a Console Program, WinForms, etc...

Upvotes: 0

Related Questions