How to handle null strings?

Question

Say I have the following code:

Request.QueryString["ids"].Split('|');

If ids is not present in the query string this will throw an exception. Is there a generally accepted way to handle this type of situation. I think all of the following options would keep this from thorwing an error, but I'm wondering if one (or some different method entirely) is generally accepted as better.

string[] ids = (Request.QueryString["ids"] ?? "").Split('|');

or

string[] ids;
if(!String.IsNullOrEmpty(Request.QueryString["ids"]))
{
   ids = Request.QueryString["ids"].Split('|')
}

or

?

I think all of these will work, but they look sort of ugly. Is there a better* way?

*better = easier to read, faster, more efficient or all of the above.

Your second option won't work, `null as string` is still null. — Lee, Dec 21 '12 at 00:34
The `If(!String.IsNullOrEmpty` one is the easiest to read - IMHO. Regarding speed is there a difference in the IL produced? — Jeremy Thompson, Dec 21 '12 at 00:35
The soft cast (qs as string) will not work. It will still return null. The null-coalesce operator (??) appears to be the 'cleanest' solution IMHO. — Jason Whitted, Dec 21 '12 at 00:35
It's generally best to validate all of your input (check that `Request.QueryString["ids"]` is non-null, throw appropriate error messages) prior to processing it (doing the `Split()`), imho, rather than combining them like that. — Carson63000, Dec 21 '12 at 00:37
Also, your first and third options are different since `ids` will be null in the third if the check fails, whereas it will be empty in the first. — Lee, Dec 21 '12 at 00:37
@Lee, actually I think in the first one it would have one element, correct? — Abe Miessler, Dec 21 '12 at 00:39
@AbeMiessler - Yes, you're right it would contain the empty string. — Lee, Dec 21 '12 at 00:41
@Lee, still a good point. Not the best example maybe, but I hope it gets the idea of what I'm asking across. — Abe Miessler, Dec 21 '12 at 00:42
Better = stating your intent clearly. If an empty string/null has no meaning, don't propogate that assumption further into your code. Test early and don't create meaningless intermediate results (such as those caused by splitting an empty string). — spender, Dec 21 '12 at 01:11
Almost all cases of NullReferenceException are the same. Please see "[What is a NullReferenceException in .NET?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-in-net)" for some hints. — John Saunders, Dec 21 '12 at 01:15

McGarnagle · Accepted Answer · 2012-12-21T01:18:46.020

12

I like using an extension method for this:

public static string EmptyIfNull(this string self)
{
    return self ?? "";
}

Usage:

string[] ids = Request.QueryString["ids"].EmptyIfNull().Split('|');

edited Dec 21 '12 at 01:18

answered Dec 21 '12 at 00:39

McGarnagle

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1

I don't like this. Null isn't an empty string and leads to a spurious entry in the split array. The better approach is to handle the null there and then and not to leave any assumptions to be dealt with downstream. – spender Dec 21 '12 at 01:04
2

`Split()` returns a `string[]`. `ToArray` isn't necessary. – spender Dec 21 '12 at 01:05

score 1 · Answer 2 · answered Dec 21 '12 at 00:39

1

Personally I'd use

string idStr = Request.QueryString["ids"];
ids = idStr == null ? new string[0] : idStr.Split("|");

answered Dec 21 '12 at 00:39

Lee

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Good. No spurious entry caused by empty strings. +1. If it were me, I'd probably test for `string.IsNullOrEmpty`, but it's not clear whether an empty string represents a useful value to the OP. – spender Dec 21 '12 at 01:06

score 0 · Answer 3 · answered Dec 21 '12 at 00:39

string[] ids = (Request.QueryString["ids"] as string).Split('|');

This will fail in the same manner as Request.QueryString["ids"]

string[] ids;
if(!String.IsNullOrEmpty(Request.QueryString["ids"]))
{
   ids = Request.QueryString["ids"].Split('|')
}

Heavier and may call the data retrieval logic twice (and you might have side-effects done twice by error) => use a temporary to store the data but heavier.

string[] ids = (Request.QueryString["ids"] ?? "").Split('|');

Definetely the easiest, cleanest and more efficient way as the compiler will generate a temporary itself.

If you encounter this kind of processing a lot of time you can build your own plumbing library with a bunch of methods with fluent names and behaviors.

How to handle null strings?

3 Answers3