C# for comparing two lists that may contain null values-CodePudding

I am comparing two excel sheets using C#.

I have assigned the sheets to datatables and I hope to compare the values in each cell. I have converted the datatables to lists and I'm iterating through them comparing them. How do I avoid a NullReferenceException if one of the values contains a null?

I am hitting a NullReferenceException at this point in the code:

    if (lst1[i].ToString() != lst2[j].ToString())

Is there a way to guard against nulls here or do I need to handle null values earlier in the code?

Thanks

CodePudding user response：

One good way to do this is to ask if the value is null before call .ToString().

So, would be like:

if (lst1[i] != null && lst2[j] != null && lst1[i].ToString() != lst2[j].ToString())

CodePudding user response：

if (lst1[i]?.ToString() != lst2[j]?.ToString())

More info on the ?. operator

CodePudding user response：

Just test for null before dereferencing lst1[i] and lst2[j]

if(lst1[i] is not null and lst2[j] is not null)
{
     if (lst1[i].ToString() != lst2[j].ToString())
     {
         ...
     }

}