CSV Validation in C# - Making sure each row has the same number of commas

I wish to implement a fairly simple CSV checker in my C#/ASP.NET application - my project automatically generates CSV's from GridView's for users, but I want to be able to quickly run through each line and see if they have the s开发者_StackOverflow中文版ame amount of commas, and throw an exception if any differences occur. So far I have this, which does work but there are some issues I'll describe soon:

 int? CommaCount = null;

StringBuilder sb = new StringBuilder();
            StringWriter sw = new StringWriter(sb);
            String Str = null;

            //This loops through all the headerrow cells and writes them to the stringbuilder
            for (int k = 0; k <= (grd.Columns.Count - 1); k++)
            {
                sw.Write(grd.HeaderRow.Cells[k].Text + ",");    
            }

            sw.WriteLine(",");


            //This loops through all the main rows and writes them to the stringbuilder
            for (int i = 0; i <= grd.Rows.Count - 1; i++)
            {
                StringBuilder RowString = new StringBuilder();
                for (int j = 0; j <= grd.Columns.Count - 1; j++)
                {
                    //We'll need to strip meaningless junk such as <br /> and &nbsp;
                    Str = grd.Rows[i].Cells[j].Text.ToString().Replace("<br />", "");
                    if (Str == "&nbsp;")
                    {
                        Str = "";
                    }

                    Str = "\"" + Str + "\"" + ",";

                    RowString.Append(Str);
                    sw.Write(Str);
                }
                sw.WriteLine();

                //The below code block ensures that each row contains the same number of commas, which is crucial
                int RowCommaCount = CheckChar(RowString.ToString(), ',');
                if (CommaCount == null)
                {
                    CommaCount = RowCommaCount;
                }
                else
                {
                    if (CommaCount!= RowCommaCount)
                    {
                        throw new Exception("CSV generated is corrupt - line " + i + " has " + RowCommaCount + " commas when it should have " + CommaCount);
                    }
                }
            }

            sw.Close();

And my CheckChar method:

protected static int CheckChar(string Input, char CharToCheck)
    {
        int Counter = 0;
        foreach (char StringChar in Input)
        {
            if (StringChar == CharToCheck)
            {
                Counter++;
            }
        }
        return Counter;
    }

Now my problem is, if a cell in the grid contains a comma, my check char method will still count these as delimiters so will return an error. As you can see in the code, I wrap all the values in " characters to 'escape' them. How simple would it be to ignore commas in values in my method? I assume I'll need to rewrite the method quite a lot.

---

var rx = new Regex("^  (  ( \"[^\"]*\" )  |  (  (?!$)[^\",]  )+  |  (?<1>,)  )*  $", RegexOptions.ExplicitCapture | RegexOptions.IgnorePatternWhitespace | RegexOptions.Multiline);
var matches = rx.Matches("Hello,World,How,Are\nYou,Today,This,Is,\"A beautiful, world\",Hi!");

for (int i = 1; i < matches.Count; i++) {
    if (matches[i].Groups[1].Captures.Count != matches[i - 1].Groups[1].Captures.Count) {
        throw new Exception();
    }
}

---

You could just use a regular expression that matches one item and count the number of matches in your line. An example of such a regex is the following:

var itemsRegex =
    new Regex(@"(?<=(^|[\" + separator + @"]))((?<item>[^""\" + separator +
        @"\n]*)|(?<item>""([^""]|"""")*""))(?=($|[\" + separator + @"]))");

---

Just do something like the following (assuming you don't want to have " inside your fields (otherwise these need some extra handling)):

protected static int CheckChar(string Input, char CharToCheck, char fieldDelimiter)
{
    int Counter = 0;
    bool inValue = false;
    foreach (char StringChar in Input)
    {
        if (StringChar == fieldDelimiter)
            inValue = !inValue;
        else if (!inValue && StringChar == CharToCheck)
            Counter++;
    }
    return Counter;
}

This will cause inValue to be true while inside fields. E.g. pass '"' as fieldDelimiter to ignore everything between "...". Just note that this won't handle escaped " (like "" or \"). You'd have to add such handling yourself.

---

Instead of checking the resulting string (the cake) you should check the fields (ingredients) before you concatenate (mix) them. That would give you the change to do something constructive (escaping/replacing) and throwing an exception only as a last resort.

In general, "," are legal in .csv fields, as long as the string fields are quoted. So internal "," should not be a problem, but the quotes may well be.