Find UserUnit in a PDF file in c++

Question

I need to get the UserUnit value from a PDF file with c++.

I'm able to do that in C# with the code below:

PdfReader reader = new iTextSharp.text.pdf.PdfReader(filename);
for (int i = 1; i <= reader.NumberOfPages; i++)
{
    PdfDictionary pageDict = reader.GetPageN(i);
    PdfNumber userUnit = pageDict.GetAsNumber(PdfName.USERUNIT);
}

How can i do that in c++?