index and length must refer to a location within the string?

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Hi, i want to read a text file, line by line. My program reads first line, then (when they like to read second line) they give mi the exception: "index and length must refer to a location within the string".

Code:

C#

try
 {
     using (StreamReader sr = new StreamReader(pot))
     {
         string line= string.Empty;
         while ((line=sr.ReadLine())!=null)
         {

             DASObject dfsa  = new DASObject();

             if (line.Substring(0, 1) == "P")
             {
                 someObject.par= true;
             }
  }}}
 catch (Exception e)
 {
     Console.WriteLine("Error: " + e.Message);
 }

The program return exception in line:

C#

if (line.Substring(0, 1) == "P")

Please help! Thanks :)

Posted 6-Jan-14 7:08am

vezo11

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Comments

Thomas Daniels 6-Jan-14 13:10pm

Is line empty when the exception occurs?

vezo11 6-Jan-14 13:21pm

Yes, its empty... First time its ok, but second time its empty.

5 solutions

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Ron Beyer · Accepted Answer · 2014-01-06T07:20:00

C#

DASObject dfsa  = new DASObject();
 
                        if (line.Substring(0, 1) == "P")
                        {
                            someObject.par= true;
                        }

Should be re-written as:

C#

DASObject dfsa  = new DASObject();
 
                        if (!string.IsEmptyOrNull(line) && line.Substring(0, 1) == "P")
                        {
                            someObject.par= true;
                        }

Which will take care of the line being a null value or if it is empty. Otherwise your first "if" statement is assuming that the line contains something. Your data file has blank lines and blank lines can't be sub-string'ed.

bowlturner · Accepted Answer · 2014-01-06T07:16:00

Solution 1

That means the line has no characters. you have a string of 0 length. You'll have to add a line.Length > 0 && into the if statement or make it a different if to handle a different situation first.

Posted 6-Jan-14 7:16am

bowlturner

Updated 6-Jan-14 7:26am

v2

Abhinav S · Accepted Answer · 2014-01-06T07:18:00

Solution 3

Check if string is not null and it's length is greater than 0.
If yes, then apply the substring.

Posted 6-Jan-14 7:18am

Abhinav S

Updated 6-Jan-14 7:24am

v2

Adam Zgagacz · Accepted Answer · 2014-01-06T07:18:00

Solution 2

Obviously you hit an empty line. You have to check whether the line has at least one character if you want to read the first character from it.
This will fix it:

C#

if  (!string.IsNullOrEmpty(line)) && (line.Substring(0, 1) == "P")
{
    someObject.par= true;
}

Posted 6-Jan-14 7:18am

Adam Zgagacz

Updated 6-Jan-14 7:23am

v2

Comments

Thomas Daniels 6-Jan-14 13:22pm

+5!

vezo11 6-Jan-14 14:19pm

Thank you all! :) (y)

Now i have another question.. if i add line, like this
someObject.param= Convert.ToInt64(line.Substring(4, 8));

then program give mi same exception.. How can i resolve this problem, with empty strings?

Adam Zgagacz 6-Jan-14 14:33pm

1) Before doing conversion you should check if line is at least 13 characters long.
2) Instead of ConvertToInt64 I would rather recommend to use long.TryParse(). With it you can handle cases when substring contains invalid characters.

vezo11 6-Jan-14 14:46pm

ok thanks :) but i don't know where is the problem, because none of line (in txt file) is not empty..

vezo11 6-Jan-14 15:01pm

i know what is problem.. the streamreader doesnt read second line, its always null. i dont know where is the problem, if i have code, like this:

using (StreamReader sr = new StreamReader(path))
{
string line= string.Empty;
while ((line= sr.ReadLine()) != null)
{... ... ...}
}

Adam Zgagacz 6-Jan-14 15:30pm

Perhaps you shous post the new question with most current code and sample of the file you are attempting to read.

vezo11 6-Jan-14 16:15pm

Ok, i found where the problem was.. in notepad, document has filled each row, in other program - every second.. :) thanks

tmazur · Accepted Answer · 2014-01-06T07:21:00

Solution 5

My best guess is that there is a carraige return for that line

Posted 6-Jan-14 7:21am

tmazur