Here are three Extension Methods which let you use the Left, Mid and Right Methods from VB6 in C# and VB.NET. The Extension Methods simply wrap the on-board .NET Framework Method Substring. These Extension Methods are now part of the Fesslersoft.Extensions.

Samples

C# Sample

#region

using System;

#endregion

namespace de.Fesslersoft.Extensions
{
    public static class Extensions
    {
        public static String Left(this string input, int length)
        {
            var result = "";
            if ((input.Length <= 0)) return result;
            if ((length > input.Length))
            {
                length = input.Length;
            }
            result = input.Substring(0, length);
            return result;
        }

        public static String Mid(this string input, int start, int length)
        {
            var result = "";
            if (((input.Length <= 0) || (start >= input.Length))) return result;
            if ((start + length > input.Length))
            {
                length = (input.Length - start);
            }
            result = input.Substring(start, length);
            return result;
        }

        public static String Right(this string input, int length)
        {
            var result = "";
            if ((input.Length <= 0)) return result;
            if ((length > input.Length))
            {
                length = input.Length;
            }
            result = input.Substring((input.Length - length), length);
            return result;
        }
    }
}

VB.NET Sample

Imports System

Namespace de.Fesslersoft.Extensions
	Public Friend Module Extensions

		<System.Runtime.CompilerServices.Extension> _
		Public Function Left(input As String, length As Integer) As [String]
			Dim result = ""
			If (input.Length <= 0) Then
				Return result
			End If
			If (length > input.Length) Then
				length = input.Length
			End If
			result = input.Substring(0, length)
			Return result
		End Function

		<System.Runtime.CompilerServices.Extension> _
		Public Function Mid(input As String, start As Integer, length As Integer) As [String]
			Dim result = ""
			If ((input.Length <= 0) OrElse (start >= input.Length)) Then
				Return result
			End If
			If (start + length > input.Length) Then
				length = (input.Length - start)
			End If
			result = input.Substring(start, length)
			Return result
		End Function

		<Runtime.CompilerServices.Extension> _
		Public Function Right(input As String, length As Integer) As [String]
			Dim result = ""
			If (input.Length <= 0) Then
				Return result
			End If
			If (length > input.Length) Then
				length = input.Length
			End If
			result = input.Substring((input.Length - length), length)
			Return result
		End Function
	End Module
End Namespace

Compatibility (as Extension method):
.NET 2.0 .NET 3.0 .NET 3.5 .NET 4.0 .NET 4.5

Compatibility (Non-Extension method):
.NET 2.0 .NET 3.0 .NET 3.5 .NET 4.0 .NET 4.5

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Related links:

• Visual Basic 6 String Functions
• String.Substring Method
• Extension Methods (C# Programming Guide)
• Fesslersoft-Extensions (GITHUB)
• FesslerSoft.Extensions (NUGET)