#nullable enable

using System;

using FileHelpers;

public class Program

{

    public static void Main()

    {

        var dto = new Dto() { PropA = "A", PropB = "B", PropC = "C", PropD = "D" };

        var engine = new DelimitedFileEngine(typeof(Dto));

        string line = engine.WriteString(new [] { dto });

        Console.WriteLine(line);

    }

}

​

[DelimitedRecord("")]

public class Dto

{

    // won't be padded

    public string? PropA { get; set; }

    // won't be padded

    public string? PropB { get; set; }

    // padded to 10

    [FieldConverter(typeof(PadStringConverter), 10)]

    public string? PropC { get; set; }

    // padded to 10

    [FieldConverter(typeof(PadStringConverter), 10)]

    public string? PropD { get; set; }

}

​

public class PadStringConverter : ConverterBase

{

    public int Width { get; private set; }

    public PadStringConverter(int width) => Width = width;

​

    public override object StringToField(string from)

    {

        return from;

    }

​

    public override string? FieldToString(object fieldValue)

    {

        return fieldValue?.ToString().PadRight(Width);

    }  

}