Initialize List With Null C#

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• C# Initialize List With Null Values
• C Sharp Initialize List
• C# Empty List

• How to initialize var? 11 answers

I want to assign a variable to an initial value of null, and assign its value in the next if-else block, but the compiler is giving an error,

Implicitly-typed local variables must be initialized.

How could I achieve this?

Peter Mortensen

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Nikhil ChavanNikhil Chavan

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C# Initialize List With Null Values

marked as duplicate by nawfal, vcsjones, iandotkelly, Selman Genç, Jim LewisJan 17 '14 at 5:08

This question has been asked before and already has an answer. Materi ukt merpati putih. If those answers do not fully address your question, please ask a new question.

2 Answers

var variables still have a type - and the compiler error message says this type must be established during the declaration.

The specific request (assigning an initial null value) can be done, but I don't recommend it. It doesn't provide an advantage here (as the type must still be specified) and it could be viewed as making the code less readable:

Which is still 'type inferred' and equivalent to:

The compiler will not accept var x = null because it doesn't associate the null with any type - not even Object. Using the above approach, var x = (Object)null would 'work' although it is of questionable usefulness.

Generally, when I can't use var's type inference correctly then

1. I am at a place where it's best to declare the variable explicitly; or
2. I should rewrite the code such that a valid value (with an established type) is assigned during the declaration.

The second approach can be done by moving code into methods or functions.

user2246674user2246674

The var keyword in C#'s main benefit is to enhance readability, not functionality. Technically, the var keywords allows for some other unlocks (e.g. use of anonymous objects), but that seems to be outside the scope of this question. Every variable declared with the var keyword has a type. For instance, you'll find that the following code outputs 'String'.

Furthermore, the code above is equivalent to:

The var keyword is simply C#'s way of saying 'I can figure out the type for myString from the context, so don't worry about specifying the type.'

var myVariable = (MyType)null or MyType myVariable = null should work because you are giving the C# compiler context to figure out what type myVariable should will be.

For more information:

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Steven WexlerSteven Wexler

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How can I initialize an empty list as a private member in a C++ class? I don't want to prompt the user to pass in an empty list, but rather just create one when I make a new instance of the class.

header.h

MyClass.cpp

This doesn't work as written, what am I missing here?

LBaelishLBaelish

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2 Answers

You don't need to do anything. The default constructor, like the name suggests, is called by default. So this is already correct:

If you want to still have myList in the member initializer list, you can do that by simply providing empty parens:

BarryBarry

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If you want to optionally hand in a user-defined value, you can use the initializer list of your constructor. Additionally, default the list to an empty content.

user1357959

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I am creating a new C# List (List<double>). Is there a way, other than to do a loop over the list, to initialize all the starting values to 0?

Peter Mortensen

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JasCavJasCav

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6 Answers

In addition to the functional solutions provided (using the static methods on the Enumerable class), you can pass an array of doubles in the constructor.

This works because the default value of an double is already 0, and probably performs slightly better.

Michael MeadowsMichael Meadows

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You can use the initializer:

So you could be using this:

Otherwise, using the default constructor, the List will be empty.

Peter Mortensen

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Jhonny D. Cano -Leftware-Jhonny D. Cano -Leftware-

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Peter Mortensen

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SLaksSLaks

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One possibility is to use Enumerable.Range:

Another is:

jasonjason

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A bit late, but maybe still of interest:Using LINQ, try

var initializedList = new double[10].ToList()

..hopefully avoiding copying the list (that's up to LINQ now).

This should be a comment to Michael Meadows' answer, but I'm lacking reputation.

MickyD

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DanielDaniel

For more complex types:

from here: David Hayden's Blog

ColinColin

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Simple syntactic c# question is this.

Shadow of the tomb raider hidden city challenges 2016. Sep 14, 2018 - Dunkin' Bones (Hidden City). If there's one thing there's definitely a lot of in Shadow of the Tomb Raider, it's skeletons. So the thought of finding.

Given this code:

It can be reduced to:

But can I get it shorter still, since they're all being initialised to an empty list?

Thank you all!

Adrian HandAdrian Hand

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4 Answers

I can recommend to use var keyword if these variables are not class fields, because types are know from usage. It really makes no sense to flat declaration of three variables.

Yes, you can do things, like declaring multiple local variables in one line and then initializing them in one line. But please, avoid declaring multiple variables in one line - it makes code much readable.

Ilya IvanovIlya Ivanov

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Purely as a point of trivia/code golf: Best file recovery software for android.

But it would be ridiculous to use this in place of the much clearer constructs available. It might have value if the initialization was more complex, and the code was properly named and spaced.

Tim MedoraTim Medora

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You can't shorten anymore.

You could use some kind of 'empty list factory':

Honestly, you probably don't want to shorten your code. Just write something readable and maintainable:

ken2kken2k

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This is not a great practice, but if you're initializing string lists a lot within a single .cs file, you can add an alias for the class with the file's other using statements:

And then the code to declare and initialize them would be:

C Sharp Initialize List

JLRisheJLRishe

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C# Empty List

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