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
– Lee, Commented Dec 21, 2012 at 0:34
The If(!String.IsNullOrEmpty one is the easiest to read - IMHO. Regarding speed is there a difference in the IL produced? — Jeremy Thompson
– Jeremy Thompson, Commented Dec 21, 2012 at 0:35
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
– Jason Whitted, Commented Dec 21, 2012 at 0:35
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
– Lee, Commented Dec 21, 2012 at 0:37

McGarnagle · Accepted Answer · 2012-12-21 01:18:46Z

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, 2012 at 1:18

answered Dec 21, 2012 at 0:39

McGarnagle

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2 Comments

spender Over a year ago

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 Over a year ago

Split() returns a string[]. ToArray isn't necessary.

Lee · Accepted Answer · 2012-12-21 00:39:46Z

1

Personally I'd use

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

answered Dec 21, 2012 at 0:39

Lee

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1 Comment

spender Over a year ago

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.

Pragmateek · Accepted Answer · 2012-12-21 00:39:03Z

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.

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