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I instantiate an array like this:
int array[] = new int[4]; What are the default values for those four members? Is it null, 0 or not exists?
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When an array is created without assigning it any elements, compiler assigns them the default value. Following are the examples: Boolean - false. int - 0.
For char arrays, the default value is '\0' . For an array of pointers, the default value is nullptr . For strings, the default value is an empty string "" . That's all about declaring and initializing arrays in C/C++.
Using default values in initialization of arrayFor double or float , the default value is 0.0 , and the default value is null for string.
It's 0. It can't be null, as null isn't a valid int value.
From section 7.6.10.4 of the C# 5 specification:
All elements of the new array instance are initialized to their default values (§5.2).
And from section 5.2:
The default value of a variable depends on the type of the variable and is determined as follows:
- For a variable of a value-type, the default value is the same as the value computed by the value-type’s default constructor (§4.1.2).
- For a variable of a reference-type, the default value is null.
Initialization to default values is typically done by having the memory manager or garbage collector initialize memory to all-bits-zero before it is allocated for use. For this reason, it is convenient to use all-bits-zero to represent the null reference.
(As an implementation detail, there's some trickiness around the first bullet point. Although C# itself doesn't allow you to declare a parameterless constructor for value types, you can create your own parameterless constructors for value types in IL. I don't believe those constructors are called in array initialization, but they will be called in a new X() expression in C#. It's outside the realm of the C# spec though, really.)
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