Question

Need some ideas how to solve this problem.
I have a template file what describes the line in the text file. For example:

Template

[%f1%]|[%f2%]|[%f3%]"[%f4%]"[%f5%]"[%f6%]

Text file

1234|1234567|123"12345"12"123456

Now i need to read in the fields from the text file. In the template file fields are described with [%some name%]. Allso in the template file there is set what the field separators are, in this example here there are | and ". The lenght of the fields can change through different files but the separators will stay the same. What would be the best way to read in the template and by template read in the text file?

EDIT: Text file has multiple rows, like this:

1234|1234567|123"12345"12"123456"\r\n
1234|field|123"12345"12"asdasd"\r\n
123sd|1234567|123"asdsadf"12"123456"\r\n
45gg|somedata|123"12345"12"somefield"\r\n

EDIT2: Ok, lets make it even harder. Some fields can contain binary data and i know the starting and end position of the binary data field. I should be able to mark those fields in the template and then the parser will know that this field is binary. How to solve this problem?

Answer 1

I would create a regex based on the template and then parse the text file using that:

class Parser
{
    private static readonly Regex TemplateRegex =
        new Regex(@"\[%(?<field>[^]]+)%\](?<delim>[^[]+)?");

    readonly List<string> m_fields = new List<string>();
    private readonly Regex m_textRegex;

    public Parser(string template)
    {
        var textRegexString = '^' + TemplateRegex.Replace(template, Evaluator) + '$';
        m_textRegex = new Regex(textRegexString);
    }

    string Evaluator(Match match)
    {
        // add field name to collection and create regex for the field
        var fieldName = match.Groups["field"].Value;
        m_fields.Add(fieldName);
        string result = "(.*?)";

        // add delimiter to the regex, if it exists
        // TODO: check, that only last field doesn't have delimiter
        var delimGroup = match.Groups["delim"];
        if (delimGroup.Success)
        {
            string delim = delimGroup.Value;
            result += Regex.Escape(delim);
        }
        return result;
    }

    public IDictionary<string, string> Parse(string text)
    {
        var match = m_textRegex.Match(text);
        var groups = match.Groups;

        var result = new Dictionary<string, string>(m_fields.Count);

        for (int i = 0; i < m_fields.Count; i++)
            result.Add(m_fields[i], groups[i + 1].Value);

        return result;
    }
}