Index and length must refer to a location within the string.parameter name: length

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public override void CreateNewOutputRows()
{
StreamReader sr = new StreamReader(fullFilePath);

int lineIndex = 0;
string line;
while (!sr.EndOfStream)
{
line = sr.ReadLine();

if (line.Substring(0,1).ToString() == "P")
{
HeaderBuffer.AddRow();
HeaderBuffer.Indicator = line.Substring(0,1).ToString();
}

lineIndex = lineIndex + 1;

}
sr.Close();
}

What I have tried:

I just need to read the header line 1st character from a flat file and write to table.
Please help why am I getting this error "Index and length must refer to a location within the string. Parameter name: length ".

Thanks

Posted 6-Jul-18 11:02am

Jk19

Updated 6-Jul-18 14:01pm

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j snooze 6-Jul-18 17:07pm

pretty sure if you debug this and look at the value in your "line" variable its probably blank. So substring function yelling at you saying the index of 0 and length of 1 doesn't exist. You'll only find that out by debugging.

Jk19 7-Jul-18 23:44pm

Thanks for the quick reply Snooze!

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Dave Kreskowiak · Accepted Answer · 2018-07-06T13:55:00

You could have easily found this if you just ran the code under the debugger.

Your code is treating every line of the text file you're reading as if it had ONE OR MORE characters in it. That's just not the case. You've got blank lines in your file that have a length of 0, hence, the exception you're getting.

Now, what are you going to do about it? How about checking for a length of 0 before you do anything with the line?

Patrice T · Accepted Answer · 2018-07-06T14:01:00

Quote:
why am I getting this error "Index and length must refer to a location within the string. Parameter name: length ".

The error message tells you that you try to substring outside of the string.
In

C#

line.Substring(0,1).ToString()

you forgot to check that line contain at least 1 char.
With the debugger, you can watch the program as it perform.

Your code do not behave the way you expect, and you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.
Debugger - Wikipedia, the free encyclopedia[^]
Debugging C# Code in Visual Studio - YouTube[^]
The debugger is here to only show you what your code is doing and your task is to compare with what it should do.

Index and length must refer to a location within the string.parameter name: length

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