C# 尝试/捕获问题

Question

So, writing a program to read a text file, then double the number and write to a different text file. Even though it is in a try/catch block, it seems that if the input file name does not match a preexisting file name, I get a loping error, instead of the error being caught and handled correctly. Here is my code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

namespace ICA28
{
class Program
{
    static void Main(string[] args)
    {
        string slInput;
        Console.Write("Please enter the input name: ");
        string sOpen = Console.ReadLine();
        sOpen = sOpen + ".txt";
        Console.WriteLine();
        Console.Write("Please enter the output name: ");
        string sSave = Console.ReadLine();
        sSave = sSave + ".txt";
        StreamReader srRead;
        StreamWriter swWrite;
        bool bError = true;
        while (bError == true)
        {
            try
            {
                srRead = new StreamReader(sOpen);
                swWrite = new StreamWriter(sSave);
                while (bError == true)
                {
                    try
                    {
                        while ((slInput = srRead.ReadLine()) != null)
                        {
                            double dDoub = double.Parse(srRead.ReadLine());
                            dDoub = dDoub * 2;
                            swWrite.WriteLine(dDoub);
                        }
                        swWrite.Close();
                        srRead.Close();
                        bError = false;
                    }

                    catch (Exception e)
                    {
                        Console.WriteLine("Error! {0}", e.Message);
                        bError = true;
                    }
                }
            }
            catch (Exception e)
            {
                Console.WriteLine("Error! {0}", e.Message);
                bError = true;
            }
        }
    }
}

}

Answer 1

在 catch 块中将 bError 设置为false 。

Answer 2

You are reading two times inside the loop. While the first read is checked for null, the second one is taken for granted but this surely will break your code if you have only one line (or an odd number of lines in the input stream)

    string slInput;
    Console.Write("Please enter the input name: ");
    string sOpen = Console.ReadLine();
    sOpen = sOpen + ".txt";
    if(!File.Exists(sOpen))
    {
        Console.WriteLine("Input file doesn't exist");
        return;  // Exit or put some kind of retry to ask again the input file
    }
    Console.WriteLine();
    Console.Write("Please enter the output name: ");
    string sSave = Console.ReadLine();
    sSave = sSave + ".txt";

   try
   {
        using(StreamReader srRead = new StreamReader(sOpen))
        using(StreamWrite swWrite = new StreamWriter(sSave))
        {
            while ((slInput = srRead.ReadLine()) != null)
            {
                double dDoub = double.Parse(slInput);
                dDoub = dDoub * 2;
                swWrite.WriteLine(dDoub);
            }
        }
    }
    catch (Exception e)
    {
         Console.WriteLine("Error! {0}", e.Message);
    }

Notice that I have put your two streams inside a using block, so, if you get an exception they are closed and disposed correctly.

Also, just one external try catch could handle all the excpetions reaised by the internal loop including possible errors when opening the files. So, unless you need to break out after the first line, you don't need any complex state logic to exit from your loop