EN CSharp Directive Warning

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Compiler message

Handbook C# · Practical Guide

Adds an author-supplied compiler warning. Compilation continues unless warnings are treated as errors.

Simple example (Example.cs)

Save this example separately as Example.cs. Run it independently of the other examples on this page.

Example.cs:

// PROJECT-EXAMPLE
#warning Review this example
System.Console.WriteLine("Ready");

Result:

Ready

Syntax

#warning message

Example 1

#warning Review the sample configuration
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        Console.WriteLine("Ready");
    }
}

Example 2

#define SAMPLE
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        #if SAMPLE
        #warning Sample mode is active
        #endif
        Console.WriteLine("Mode selected");
    }
}

Official source: Microsoft Learn.