C# Entry Point Function

C# entry point function

Before C# 9, the entry point had to be declared explicitly. C# 9 introduces top level statements which allow the entry point to be generated implicitly. (Only a single source file in a project can include top-level statements, however.)

When the entry point is declared explicitly, it has to be Main. It's static because otherwise the CLR would need to worry about creating an instance of the type - which means you'd presumably have to have a parameterless constructor, even if you didn't want an instance of the type, etc. Why would you want to force it to be an instance method?

Even with top-level statements, your actual program still has an entry point called Main - it just doesn't appear in your source code.

Can I determine my own entry point method for C#

No. The static Main() is the only entry point for C#, and all other functions should be called from it.

What is the entry point of .net executable?

Every console or windows application normally uses the Main() method to execute. This has to be static and looks like this:

public static void Main() {
    // your code
}

You can provide arguments.

The documentation states that

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.

The mentioned parameter allows to specify the type containing the Main method. Still it has to be the Main. So it is necessary you name it like this.

See this question: C# entry point function for more information on the Main() and documentation for additional information.

How to put the entry point of an Azure Function inside a .NET DLL?

As of the writing of this question, it was not supported, but now it is!

https://github.com/Azure/azure-webjobs-sdk-script/wiki/Precompiled-functions

Excerpt from wiki:

{
"scriptFile": "PreCompiledFunctionSample.dll",
"entryPoint": "PreCompiledFunctionSample.MyFunction.Run",
"bindings": [
    {
        "authLevel": "function",
        "name": "req",
        "type": "httpTrigger",
        "direction": "in"
    },
    {
        "name": "$return",
        "type": "http",
        "direction": "out"
    }
],
"disabled": false
}

What is the entry point of a WPF application?

Your main entry point is an override of OnStartup in the code-behind of App.Xaml :

public partial class App : Application
{
    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);
        // here you take control
    }
}

Other points of interest might be Application.OnActivate() and the Loaded and Initialized events of your MainWindow.

If I have to start some threads or services, where should write the code for starting them?

Depends on what those threads/services need and want.

How can I change the starting point in C# within same class?

You can only have one entry (Main) point. Your Main method's signature should match either with Main() or Main(string[]) (actually there are more valid signatures. You can check them by going by the link at the bottom), so you can have only one of them in your code. If the signature is different from Main() or Main(string[]), then it is not considered as an entry point.

For example, you can have:

// Will compile. Warning CS0028  'Program.Main(int)' has the wrong signature to be an entry point.

static void Main() // Entry point
{
}

static void Main(int n) // Not an entry point
{
}

But you can't use:

// Compiler Error CS0017 Program has more than one entry point defined.

static void Main() // Entry point
{
}

static void Main(string[] args) // Another entry point
{
}

For more information, please check Main() and command-line arguments (C# Programming Guide).

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