Library for calculating GTIN from EAN-13 barcode

Question

I am creating an XML from a backend that is supposed to be fed into a GDSN datapool. The company has a very old backend which only has their own PLU number and barcode attached to every item. What I know is that (at least here in Iceland) most GTIN are the EAN-13 barcode with a padded 0 at the front although this is not always the case. Do you know of a library that could check if a GTIN is correct i.e. would calculate the check digit?

I am using a windows form and am using C#.

Answer 1

First to validate what you want to do: https://www.gs1.org/services/check-digit-calculator

Then you have 2 possibilities for GTIN since it must be 14 digits long.

• The case you described, then you pad a 0 on the left
• A GTIN with right length is provided directly (which is possible and left digit will not be 0)

Here is a quick example on how you can check this, based on the fact you know the gtin string only contains digits:

    public Boolean ValidateGTIN(string gtin)
    {
        string tmpGTIN = gtin;
        if (tmpGTIN.Length < 13)
        {
            Console.Write("GTIN code is invalid (should be at least 13 digits long)");
            return false;
        }
        else if (tmpGTIN.Length == 13)
        {
            tmpGTIN = "0" + gtin;
        }
        // Now that you have a GTIN with 14 digits, you can check the checksum
        Boolean IsValid = false;
        int Sum = 0;
        int EvenSum = 0;
        int CurrentDigit = 0;
        for (int pos = 0; pos <= 12; ++pos)
        {                
            Int32.TryParse(tmpGTIN[pos].ToString(), out CurrentDigit);
            if (pos % 2 == 0)
            {                    
                EvenSum += CurrentDigit;
            }                    
            else
            {
                Sum += CurrentDigit;
            }                    
        }
        Sum += 3 * EvenSum;
        Int32.TryParse(tmpGTIN[13].ToString(), out CurrentDigit);
        IsValid = ((10 - (Sum % 10)) % 10) == CurrentDigit;
        if (!IsValid)
        {
            Console.Write("GTIN code is invalid (wrong checksum)");
        }
        return IsValid;
    }