Concatenate column headers if value in rows below is non-blank

I have table with data in the format below.

Data

I want the finished table to have the blank column to be populated like the highlighted one below.

Finished Table

So, I need a formula or VBA that will return and concatenate the headers of non-blank cells in each row.

Use¹ the following as an array formula.

=TEXTJOIN("-->", TRUE, IF(LEN(C3:I3), C$2:I$2, ""))

Pre-Excel 2016 versions

While you could just string together a series of IF statements, a cleaner alternate might be to write a user defined function (aka UDF).

In a standard VBA module code sheet:

Function udf_Stitch_Together(r As Range, _
                             h As Range, _
                             Optional d As String = "-->", _
                             Optional blnks As Boolean = False) As String
    Dim s As String, c As Long
    For c = 1 To r.Cells.Count
        If CBool(Len(r.Cells(c).Text)) Then _
            s = s & IIf(Len(s), d, vbNullString) & h.Cells(c).Text
    Next c
    udf_Stitch_Together = s
End Function

¹ _{The TEXTJOIN was introduced with Excel 2016 in the following versions:Excel for Android phones, Excel Mobile, Excel 2016 with Office 365, Excel 2016 for Mac, Excel Online, Excel for iPad, Excel for iPhone and Excel for Android tablet.}