C#•10mo ago

No Main and class confusion in newer C# versions

I am confused about the newer C# versions... When I make a console app, it just starts like so:

// See https://aka.ms/new-console-template for more information
Console.WriteLine("Hello, World!");

// See https://aka.ms/new-console-template for more information
Console.WriteLine("Hello, World!");

As you see, theres no class or Main method. In Java, and old C# if I am correct, we always have to have a class with a main method for our code to run. However, it seems that newer C# versions doesn't require this. Yet my confusion is: - OOP is rather valuable in a lot of scenarios, so what do we do without classes? - Is the Main method just in the first file we create? or where is it? it seems to run without it

30 Replies

SinFluxx•10mo ago

https://learn.microsoft.com/en-us/dotnet/csharp/tutorials/top-level-statements

Top-level statements - C# tutorial - C#

This tutorial shows how you can use top-level statements to experiment and prove concepts while exploring your ideas

SinFluxx•10mo ago

essentially, in one file (Program.cs) in your application, you can ignore the namespace / class / Main method declaration they'll be assumed and your app will still run fine, you can always just write them back in manually, or tick the option "Do not use top level statements" when creating the project in VS

SteadhavenOP•10mo ago

So in the one first file, called EXACTLY Program.cs, we have an implicit main method. In that file, we have access to args (from the main method) even though we didn't declare it. - This means we cannot call the Program.cs file in other code? - Also, it means it is the only file that is like that - e.g. all other files needs to have a namespace/class?

SinFluxx•10mo ago

Also, it means it is the only file that is like that - e.g. all other files needs to have a namespace/class?

Correct

SteadhavenOP•10mo ago

Ah we can access the Program.cs if we declare a class in it, its just not required by default. or at least I think that is possible?

SteadhavenOP•10mo ago

SteadhavenOP•10mo ago

Hm, no it seems that its not reusable anything one writes in that file

They in fact shouldnt even be in Program.cs

Still, it seems like Program.cs can't have classes (even if one shouldn't have it anyhow), since it seems to wrap everything in an implicit "Main" method

Top Level Statements work with any file name

So if I have multiple files without an entry method (Main), as well as all of them being Top Level Statements, then I will get errors and it won't work? E.g. only one file is allowed to use Top Level Statements, if I didn't explcitly write a Main method myself somewhere? Aha, so if I make a class (or similar things) then it auto assumes that this should not be included in the Main Method. Its smart enough to differentiate between Top Level Statements, and things like declaring classes which are not a Top Level Statement

Pobiega•10mo ago

It is recommended to not add a bunch of classes to your top-level-statements file, since it gets messy but you can. for a tiny console app, you might stick some records in there the order is also very important

SteadhavenOP•10mo ago

Right, so I can but it is not recommended. If I have a Main method explictly declared somewhere (not Program.cs), can I then have multiple Top Level Statement files?

Pobiega•10mo ago

if you declare anything before a statement is used, the compiler disabled top level mode no

SteadhavenOP•10mo ago

Ah makes sense

Pobiega•10mo ago

if you have an explicit Main, you cant have any TLS files

SteadhavenOP•10mo ago

Aaah

Pobiega•10mo ago

please dont try and "abuse" TLS its meant for simple short startup methods

SteadhavenOP•10mo ago

now I get it. So ONE file with TLS at MOST, and it is not recommended to include extra things like classes etc in that file

Pobiega•10mo ago

like, creating a host builder, configuring it, building it, running the host pretty much yep

SteadhavenOP•10mo ago

Thanks makes sense :) ohhh sorry, one last quesiton. Is the TLS file always included in the Namespace and/or solution that I am writing in?

Pobiega•10mo ago

nope it has a global namespace iirc

SteadhavenOP•10mo ago

ok thanks

Pobiega•10mo ago

you should never have to refer back to it however so it shouldnt be a problem

SteadhavenOP•10mo ago

yea true thanks

Pobiega•10mo ago

the only "smart" thing the compiler does with TLS files is figure out if args should be available or not, and if it returns a void or an int oh and if it should be async Task or not

SteadhavenOP•10mo ago

True, this thing messed with me also that in C# we can have main method with int or void lol

Pobiega•10mo ago

it just "picks" the "right" main from the list of $mains

MODiX•10mo ago

The possible signatures for Main are

public static void Main() { }
public static int Main() { }
public static void Main(string[] args) { }
public static int Main(string[] args) { }
public static async Task Main() { }
public static async Task<int> Main() { }
public static async Task Main(string[] args) { }
public static async Task<int> Main(string[] args) { }

public static void Main() { }
public static int Main() { }
public static void Main(string[] args) { }
public static int Main(string[] args) { }
public static async Task Main() { }
public static async Task<int> Main() { }
public static async Task Main(string[] args) { }
public static async Task<int> Main(string[] args) { }

public is not required (can be any accessibility). Top-level statements are compiled into a Main method and will use an appropriate signature depending on the body. https://docs.microsoft.com/en-US/dotnet/csharp/fundamentals/program-structure/main-command-line

Main() and command-line arguments - C#

Learn about Main() and command-line arguments. The 'Main' method is the entry point of an executable program.

SteadhavenOP•10mo ago

lol wow

Pobiega•10mo ago

99% of the time void is fine - int is useful if you want to explicitly control the errorcode

SteadhavenOP•10mo ago

hm main method seem tougher than I thought to learn. I am just used to one main method in Java (perhaps its same there, but I am ignorant of it)

Pobiega•10mo ago

useful for stuff like kubernetes its the same really

SteadhavenOP•10mo ago

Yeah ok then I won't have to worry, all of my code so far is just using main method returning void

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No Main and class confusion in newer C# versions