Getting exception when reading two lines of data from text file in C#

Question

Hello I am reading two line of data from text file in C#, and at the end of file I get error "Object reference not set to an instance of an object". I know this error is because of end of file, and object is being assigned null value. But i need to avoid this error. My code is in below format:

try
{
    sting line;
    while ((line = file.ReadLine().Trim()) != null)
    {
        //do something
        if ((line2 = file.ReadLine().Trim()) != null)
        //do something
    }
}
catch(exception e)
{
    console.write(e.Message);
}

At end of file, is where it goes in exception.

Thanks for help in advance.

If file.ReadLine() doesn't return anything, you'll get a NullReferenceException (the one you're getting) when you call Trim() — cost
– cost, Commented Jun 27, 2018 at 17:17
Two things: 1. Try to make an effort to format your code. People will be more willing to help if they can read your code. 2. Make sure the code you do provide can compile. You have a number of mistakes in the code that won't compile. For example: using sting instead of string. console.write should be capitalized: Console.Write — Chris Dunaway
– Chris Dunaway, Commented Jun 27, 2018 at 21:45

TrueWill · Accepted Answer · 2018-06-27 17:50:41Z

2

The issue is that the code is calling Trim() on the result of the ReadLine() before checking if the result is null.

From How to: Read a Text File One Line at a Time (Visual C#):

while((line = file.ReadLine()) != null)  
{
    // Do something with line
}

Also note that it's generally best to avoid calling ReadLine() again within the loop.

edited Jun 27, 2018 at 17:50

answered Jun 27, 2018 at 17:17

TrueWill

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Comments

user4610426 · Accepted Answer · 2018-06-27 17:24:44Z

1

Use the ?. operator, like:

file.ReadLine()?.Trim()

answered Jun 27, 2018 at 17:24

user4610426

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