C#中的动态数组填充

Question

I'd like to share a very bizzare phenomenon I am currently working on. Globally speaking, the task looks trivial as it is about filling some arrays. However after debugging several times my code, the error: Index was outside the bounds of the array does not look as trivial as it looks, and I wonder if I miss something. I have hesitated before posting that thread to avoid any potential downvotes, but to be honest, this error is really weird to me, since all the defined variables retrieved from the debug mode matches my expectation.

As an illustration:

int count = FileNameFromPath.Length;
int i = 0;
while (i < count)
{
    try
    {
        string[] outp = new string[]
        {
        "CS_" + FileNameFromPath[i]
        }

        ;
        DataTable SourceData = GetDataTabletFromCSVFile(FileDirectory[i]);
        string[] SavePath = new string[]
        {
        DirOutputOlis + @"\" + outp[i]
        }

        ;
        CreateCSVFileFromDataTable(SourceData, SavePath[i]);
        Console.WriteLine("File Processed in Output Directory: {0}", outp[i]);
        i++;
    }
    catch (InvalidOperationException exc)
    {
        using (StreamWriter writer = new StreamWriter(logPath, true))
        {
            writer.WriteLine("Message :" + exc.Message + "<br/>" + Environment.NewLine + "StackTrace :" + exc.StackTrace + "" + Environment.NewLine + "Date :" + DateTime.Now.ToString());
            writer.WriteLine(Environment.NewLine + "-----------------------------------------------------------------------------" + Environment.NewLine);
        }

        Console.WriteLine("File not Processed to Directory:  {0}", FileNameFromPath);
        PrintException(exc);
        Console.WriteLine("--------------------------------------------------------------------------------\n");
        goto Exitx;
    }
}

I reiterate: outp , SourceData , SavePath , count=3 are all correct for i=0 , but the problem starts at the following increment i=1 in row SavePath even if for the latter case the former variables are correct too (from the debug mode).

Answer 1

Looks like outp is defined as a 1-element array (so, only outp[0] is valid). If i > 0, you are accessing outside the array boundaries, hence the exception. Same applies to SavePath.

Since you want to have an array of elements, you can either

1. Declare outp/Savepath outside the while cycle, specifying the correct number of elements (once declared, arrays have fixed size)
2. Declare them as a List rather than Array. A List can be accessed via the [] operator, but also supports the .Add method allowing it to grow.

You could go with something like

List<string> outp = new List<string>();
List<string> SavePath = new List<string>();

for (int i = 0; i < FileNameFromPath.Length; ++i)
{
    outp.Add("CS_" + FileNameFromPath[i]);
    SavePath.Add(DirOutputOlis + @"\" + outp[i]);
}

Answer 2

Step through your code here and imagine what happens with different values of i :

// outp is an array with a *single* element
string[] outp = new string[]
{
    "CS_" + FileNameFromPath[i]
};
DataTable SourceData = GetDataTabletFromCSVFile(FileDirectory[i]);
// SavePath is an array with a *single* element
string[] SavePath = new string[]
{
    DirOutputOlis + @"\" + outp[i]
};
CreateCSVFileFromDataTable(SourceData, SavePath[i]);
Console.WriteLine("File Processed in Output Directory: {0}", outp[i]);
i++;

Since outp and SavePath only have 1 element, you will get an exception when you try to index them when i > 0 . It's not clearly exactly what you were trying to do there. If you don't actually need an array, then just use a string. So it would become:

string outp = "CS_" + FileNameFromPath[i];

and:

string SavePath = DirOutputOlis + @"\" + outp;

Or, if your intention was to store the values of outp and SavePath , then you need a collection defined outside of the while loop:

string[] outp = new string[count];
string[] SavePath = new string[count];
// ...
while (i < count)
{
    outp[i] = "CS_" + FileNameFromPath[i];
    // ...
    SavePath[i] = DirOutputOlis + @"\" + outp[i];
    // ...
}