How to compile with /main

BenTam-3003 686

Dear All,

I got the following error.

CS0017  Program has more than one entry point defined. Compile with /main to specify the type that contains the entry point.

Could anybody tell me how to "compile with /main"?

Viorel 112.8K Reputation points

2022-02-09T10:21:48.587+00:00

Maybe it is better to rename or remove the Main functions that are not needed. Keep one Main function only.
Jack J Jun 24,296 Reputation points Microsoft Vendor

2022-02-10T01:59:47.057+00:00

@BenTam-3003 ，For better to solve the problem, I suggest that you could upload your project to OneDrive or Github, then share the link here.

Thanks for understanding.

4 answers

RLWA32 40,861

For a .Net Framework project set the Startup Object in the project properties.

Following code generates CS0017 when the Startup Object is not set -

using System;  
using System.Collections.Generic;  
using System.Linq;  
using System.Text;  
using System.Threading.Tasks;  
  
namespace TwoMain  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            Console.WriteLine("Hello from Program.Main");  
        }  
    }  
  
    class DupMain  
    {  
        static void Main(string[] args)  
        {  
            Console.WriteLine("Hello from DupMain.Main");  
        }  
  
    }  
}

Set the Startup Object in response to the error message -

BenTam-3003 686

Hi @RLWA32

I am using version 2022. I don't know how to open the window that your capture. Please tell me how.

The screen capture is as below.

The code is as follows

using System;  
using System.Collections.Generic;  
using System.Diagnostics;  
using System.Linq;  
class Test  
{  
    static void Main()  
    {  
        int size = 10000000;  
        Console.WriteLine("Always false");  
        RunTests(size, x => false);  
  
        Console.WriteLine("Always true");  
        RunTests(size, x => true);  
  
    }  
  
    static void RunTests(int size, Func<string, bool> predicate)  
    {  
        for (int i = 1; i <= 10; i++)  
        {  
            RunTest(i, size, predicate);  
        }  
    }  
  
    static void RunTest(int depth, int size, Func<string, bool> predicate)  
    {  
        IEnumerable<string> input = Enumerable.Repeat("value", size);  
  
        for (int i = 0; i < depth; i++)  
        {  
            input = input.Where(predicate);  
        }  
  
        Stopwatch sw = Stopwatch.StartNew();  
        input.Count();  
        sw.Stop();  
        Console.WriteLine("Depth: {0} Size: {1} Time: {2}ms",  
                          depth, size, sw.ElapsedMilliseconds);  
    }  
}

Castorix31 81,846 Reputation points

2022-02-09T15:39:59.48+00:00

Are you sure you have a Console project (only 1 Main() in Program.cs) ?
Karen Payne MVP 35,196 Reputation points

2022-02-09T16:17:48.837+00:00
Make sure to specify the project namespace as per below. Each class should specify the intended namespace.

Please take a screenshot of your project from Solution Explorer showing all files/classes.

namespace YourNameSpaceGoesHere { class Program { static void Main() { int size = 10000000; Console.WriteLine("Always false"); RunTests(size, x => false); Console.WriteLine("Always true"); RunTests(size, x => true); } ... } }

This is a default new console project, you removed the namespace which may be the reason for code not shown causing this issue
RLWA32 40,861 Reputation points

2022-02-09T16:22:28.21+00:00

Is there any other code in your project besides what was posted here?
BenTam-3003 686 Reputation points

2022-02-10T04:53:24.437+00:00

Hi @Castorix31

I try to run the project today. I don't know why the error suddenly disappears. Therefore the problem is solved.
BenTam-3003 686 Reputation points

2022-02-10T04:56:02.08+00:00

Hi @RLWA32

I try to run the project today. I don't know why the error suddenly disappears. Therefore the problem is solved.

Karen Payne MVP 35,196 Reputation points

2022-02-09T10:31:53.83+00:00

Perhaps you are attempting to use Top-level statements with a version of C# before C#9, examples here. Or conventional Main.
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BenTam-3003 686 Reputation points

2022-02-09T14:57:20.14+00:00

Hi @Karen Payne MVP

I am not using top-level statements. See my code above.

RLWA32 40,861 Reputation points

2022-02-09T15:30:04.943+00:00

Is there any other code in your project besides what you posted above? When I insert the posted code into a .Net Framework 4.8 project for a console application VS2019 can build the project with no compilation errors.
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Karen Payne MVP 35,196 Reputation points

2022-02-09T17:25:00.937+00:00

See the following project.
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BenTam-3003 686 Reputation points

2022-02-10T04:59:58.623+00:00

Hi @Karen Payne MVP

I try to run the project today. I don't know why the error suddenly disappears. Therefore the problem is solved.
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Bruce (SqlWork.com) 57,481 Reputation points

2022-02-09T17:35:01.923+00:00

the error means when you project is built, more than one public static main was found. when the exe is built, bootstrap code is added to call this method. as there are legimate cases of having more than one Main defined, the compile has a switch to define which one the bootstrap code should use.

in your case, it does not seem intentional. you probably have additional *.cs file in the project that define main, or you have added a reference to a dll that has a main defined.

note: if you are using the new msbuild project files, by default all *.cs files in the folder or sub folders are included in the build. for more help, you should show us the project file
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BenTam-3003 686 Reputation points

2022-02-10T05:00:54.45+00:00

Hi @Bruce (SqlWork.com)

I try to run the project today. I don't know why the error suddenly disappears. Therefore the problem is solved.
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How to compile with /main

4 answers