Unreachable code

This kind of code is never executed. The C# compiler issues an unreachable code detected warning. This warning can help you eliminate unused code.

We look at unreachable code. We see how to eliminate this error but not remove the code—pragma directives can be used for this purpose.

This C# program has some unreachable code. In the while-loop, the condition must be evaluated before the loop body is entered. In a while false loop, all the enclosed code is unreachable.

using System;

class Program
{
    static void Main()
    {
        while (false)
        {
            int value = 1;
            if (value == 2)
            {
                throw new Exception();
            }
        }
    }
}
Warning CS0162: Unreachable code detected

Example 2

Sometimes, you may not want to delete the unreachable code for some reason. If you comment it out, it will no longer be compiled. This can result in a phenomenon called "bit rot."

using System;

class Program
{
    static void Main()
    {
#pragma warning disable
        while (false)
        {
            int value = 1;
            if (value == 2)
            {
                throw new Exception();
            }
        }
#pragma warning restore
    }
}

Reachability notes

Reachability in the C# language is carefully described in the specification. The reachability and unreachability of every statement is determined based on its end point.

End points

An end point is the location immediately after a statement. If the end point of a statement is reachable, the statement itself is reachable.