CODEWITHSUNDEEP
c#arraysstringobject
user943870
user943870

Reputation: 303

How are strings stored in an object array?

object[] objs = new object[]{"one","two","three"};

Are the strings stored in the array as references to the string objects

[@] - one
[@] - two
[@] - three

or are the string objects stored in the array elements?

[one][two][three]

Thanks.

Edit: Sorry, my fancy diagram failed miserably.

Upvotes: 3

Views: 1114

Answers (4)

Adam Mihalcin
Adam Mihalcin

Reputation: 14468

Jon Skeet describes the actual implementation very well, but let's consider why it would be nonsensical for the CLR to store strings directly in an array.

The first reason is that storing strings directly in the array would harm performance. If strings were stored directly in an array, then to get to the element 1000 of the array the CLR would have to walk through the bytes of all the strings in the array until it reached element 1000, checking all the while for string boundaries. Since strings and any other reference types are stored in arrays as references, finding the right element of the array requires one multiplication, one addition, and following one pointer (the notion of a pointer here is at the implementation level, not the programmer-visible level). This produces much better performance.

The second reason that strings cannot reasonably be stored directly in an array is that C# arrays of reference type are covariant. Let's say that strings were stored directly in the array generated with

string[] strings = new string[] {"one", "two", "three"};

Then, you cast this to an object array, which is legal

object[] objs = (object[])strings;

How is the compiler supposed to generate code that takes this possibility into account? A method that takes an object array as a parameter can have a string array passed to it, so the CLR needs to know whether to index into the array as an object array, or a string array, or some other type of array. Somehow, at runtime every array would have to be marked with the type declaration of the array, and every array access would have to check the type declaration and then traverse the array differently depending on the type of the array. It's far simpler to stick with references, which allow a single implementation of array accesses and improve performance to boot.

Upvotes: 4

Mayank
Mayank

Reputation: 8852

all the primitive types are stored directly into a array but all other object or reference types are stored as memory references. This is true for all Objects not limited to Strings.

Upvotes: 1

Jon Skeet
Jon Skeet

Reputation: 1501916

String objects can never be stored directly in an array, or as any other variable. It's always references, even in a simple case such as:

string x = "foo";

Here the value of x is a reference, not an object. No expression value is ever an object - it's always either a reference, a value type value, or a pointer.

Upvotes: 5

The Beruriah Incident
The Beruriah Incident

Reputation: 3257

They're stored internally as references. A copy of the string is stored, and anywhere that string is used, there's a reference to the same stored string. (this is one of many reasons that strings are immutable; otherwise, modifying one instance of a string would modify everywhere it appeared)

Upvotes: 2

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