string filename = o.FileName;
string[] textlines = File.ReadAllLines(filename);
string[] mainAndSublines = null;
int i = 0;
foreach(string textline in textlines)
{
if (textline.Substring(0, 1) != " ")
{
i++;
}
mainAndSublines[i] = textlines[i]; //Getting error, NullReferenceException was not handled
}
I am getting thee error:
NullReferenceException was not handled
You have initialized mainAndSublines to null.
If you know the desired size in advance use this:
string[] mainAndSublines = new string[100];
If you don't know the size you want in advance, use a dynamically resizing container such as a List:
List<string> mainAndSublines = new List<string>();
<pedant>Actually he has initializes mainAndSublines to a value, explicitly - the null value. It's still a value :)</pedant>Simply because your array mainAndSublines is null and you can't access an element of an array that is null ...
You've actually got two problems here - one is that you're trying to set values into a null array, and the other is how you're trying to find whether the first character of the line is a space.
I would use a List<String> for the non-space-starting lines, as you can't tell how many there will be, but then you're assuming that every line will be non-empty. Fortunately it's easy to fix this using StartsWith.
I'd then use LINQ if you're using .NET 3.5 or higher, which makes the whole thing really simple:
List<string> mainAndSublines = File.ReadAllLines(filename)
.Where(x => !x.StartsWith(" "))
.ToList();
In .NET 4 you can make this more memory-efficient using File.ReadLines instead of File.ReadAllLines - this streams the file instead of loading the whole thing into memory to start with.
You need to initialize second array too, as you did with first, probably equal by size.
string[] mainAndSublines = new string[textlines.Length];
But the most suitable solution here will be Mark's one - auto-resizable container.