Question

public struct sFr
{
    public sFe[] errorDetails;

    public sFr(sFe[] _errorDetails)
    {
        // ?? whats code to initialise the array without getting error
        // as this throws null ref when used later from client calling this webservice

        errorDetails = _errorDetails;

        // do we need to create the array of elements which we populate ?
    }
}

Answer 1

Very simple fix; don’t make it a struct.

Sorry, but a struct there is just plain wrong…

As are public fields, and usually arrays (prefer lists)

And overly abbreviated names (use things like [XmlRoot("sFr"), XmlType("sFr")] if you need to control the serialization, but make the type-name meaningful).

Re the error; the syntax should just be this.fieldName = value;

I’d have something like:

public sealed class ErrorResult
{
    private readonly List<SomeErrorType> errors = new List<SomeErrorType>();
    public List<SomeErrorType> Errors { get { return errors; } }
    public ErrorResult() {} // make explicit so never lost
}