C# Parse value if not null

Question

Here's something that's not really an issue and I apologize if it's a stupid question but it's just something I'm curious about. Let's say I want to parse a string parameter as an integer if the string is not null, otherwise set the integer to -1. Is there a better way to write this statement:

int id = context.Request["Id"] == null ? -1 : int.Parse(context.Request["Id"]);

It just seems messy to have to evaluate the string to see if it's null and then evaluate it again to parse it. Now that I think about it, this has come up with objects and accessing an objects properties if it isn't null. So something like:

int id = person == null ? -1 : person.id;

Is this the accepted practice?

Jacob Bundgaard · Accepted Answer · 2023-12-10 01:25:26Z

12

For your first example, you can use the null coalescing operator:

int id = int.Parse(context.Request["Id"] ?? "-1");

For your second example, you can use the null-conditional operator:

int id = person?.Id ?? -1;

edited Dec 10, 2023 at 1:25

Jacob Bundgaard

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answered Jul 30, 2012 at 19:47

Mark Byers

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2 Comments

Reed Copsey Over a year ago

This does cause an unnecessary int.Parse("-1"), though, instead of just setting the value to -1 directly.

BurkDiggler Over a year ago

I didn't even think to make the null check while passing the parameter into the parse method, doh! It seems so simple now. And yes the null-safe dereferencing operator is exactly what I was looking for, good to know that it exists, just not for C#. Thanks!

psubsee2003 · Accepted Answer · 2012-07-30 19:54:35Z

3

You didn't state whether int.Parse() has the potential to fail for non-null values, but if you aren't certain a non-null input string will always be an int value, you can also use the TryParse() method:

int id;
if (!int.TryParse(context.Request["Id"], out id)
    id = -1;

This will not throw an exception if context.Request["Id"] is null, or if it is not parsable to int.

answered Jul 30, 2012 at 19:54

psubsee2003

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2 Comments

huysentruitw Over a year ago

that looks exaclty like my answer :) Seems like we were typing the same chars at exaclty the same moment.

huysentruitw Over a year ago

anyway +1 for this, as it is much better to be prepared for non-numeric input instead of catching an exception.

Reed Copsey · Accepted Answer · 2012-07-30 19:51:30Z

1

Personally, I would make this two statements:

string tmp = context.Request["Id"];
int id = String.IsNullOrWhitespace(tmp) ? -1 : int.Parse(tmp);

This handles this without any extra parsing. Doing this in one line will require an extra lookup of the context (which you were trying to avoid) or extra parsing.

answered Jul 30, 2012 at 19:51

Reed Copsey

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2 Comments

huysentruitw Over a year ago

IsNullOrWhitespace? and what with everything else that isn't a number? int.TryParse seems a better solution to me.

Reed Copsey Over a year ago

@WouterH Yes - this doesn't handle non-numeric input - but it was really more a matter of trying to address the specific question regarding handling nulls vs. int parsing.

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