尝试将字符串解析为double，得到“输入字符串格式不正确”。

Question

I need to parse a string from a datatable into a double. I have a datatable (dt) and it has different columns, and each of these columns are converted to strings with the .ToString() method. However, when I try to output the latitude and longitude of the data, I get an error "Input string was not in a correct format." So I guess my main question is, how do you parse text from an object converted to a string using the .ToString() method..

using System;
using System.IO;
using System.Collections;
using System.Data;

namespace SalesMap
{
    class SalesMap
    {
        private static DataTable InitData1()
        {
            //Datatable for entire list of zipcodes
            DataTable datat = new DataTable("DATA");
            DataColumn state = new DataColumn();
            DataColumn county = new DataColumn();
            DataColumn statecounty = new DataColumn();
            DataColumn latitude = new DataColumn();
            DataColumn longitude = new DataColumn();
            DataColumn salesperson = new DataColumn();

            //Add the columns to the datatable
            datat.Columns.Add(state);
            datat.Columns.Add(county);
            datat.Columns.Add(statecounty);
            datat.Columns.Add(latitude);
            datat.Columns.Add(longitude);
            datat.Columns.Add(salesperson);

            return datat;
        }       

        private static String InitPath()
        {
            string path = "C:/Documents and Settings/Andre/Desktop/salesmapdata/MapPointCountyLatLong.csv";
            return path;
        }

        public static void Main()
        {
            try
            {
                DataTable dt = InitData1();
                StreamReader sr = new StreamReader(InitPath());
                String csvData = string.Empty;

                while ((csvData = sr.ReadLine()) != null)
                {
                    String[] data = csvData.Split(',');
                    //dt.Rows.Add(data);
                    DataRow newRow1 = dt.NewRow();
                    newRow1[0] = data[0].ToString(); //state
                    newRow1[1] = data[1].ToString(); //county
                    newRow1[2] = data[2].ToString(); //state|county
                    newRow1[3] = data[3].ToString(); //latitude
                    newRow1[4] = data[4].ToString(); //longitude
                    newRow1[5] = data[5].ToString(); //salesperson
                    dt.Rows.Add(newRow1);

                    Console.WriteLine("Row added for: dt");
                }

                foreach (DataRow row1 in dt.Rows)
                {
                    double latitude1 = Double.Parse(row1[3].ToString());
                    double longitude1 = Double.Parse(row1[4].ToString());

                    if (row1[5].ToString() != "UNKNOWN" || row1[5].ToString() != "SALESMAN")
                    {
                        Console.WriteLine(latitude1);
                        Console.WriteLine(longitude1);
                    }
                }

                dt.WriteXml(@"c:\test\dt1.xml");
                sr.Close();
            }

            catch (Exception e)
            {
                StreamWriter sw = new StreamWriter(@"c:\test\error.txt");
                sw.WriteLine(e.Message.ToString());
                sw.Close();
            }
        }
    }
}

Answer 1

First of all, when reading data from CSV file, you don't need to call data[x].ToString() on each array element, since they are already strings.

Few potential issues you might have with Double.Parse calls:

1. The data in your CSV file is really in the wrong format (maybe you misplaced the column numbers, or data might have an additional symbols that couldn't be parsed, like Tim mentioned in his comment).
2. You have empty strings in your columns. Those cannot be parsed to double. You need to check that first, using string.IsNullOrWhitespace() or something similar.
3. Your culture is wrong. You might have latitude and longitude values that use decimal point in your CSV file, but your current thread culture might be using comma as decimal separator. There's an overload of Decimal.Parse() that accepts Culture as parameter (you could supply CultureInfo.InvariantCulture or any other CultureInfo ).