Re: Variable declaration/definition

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Jon Skeet [C# MVP] wrote:
Annonymous Coward <me@xxxxxxxx> wrote:
I am relatively new in C#, but have several years C++/Java. I am writing a little C# console app to "test the waters" and learn the language.

If I have a class defined as:

class MyClass
{
MyClass(string s1, int i2, bool b3)
{
}
}


Why can't I declare a variable on the stack somewhere later on in my code like this:

// .... code above
MyClass mc("Hello",42, true);

That's not how you invoke a constructor in C#. You can just declare a variable, of course:

MyClass mc;

but that won't create an instance.
Do I always have to alloc from the heap when instantiating objects whose ctor have parameters?

You always have to allocate from the heap whenever you create *any* objects, regardless of whether there are parameterless constructors. In that respect C# is identical to Java. Basically C# is closer to Java than it is to C++ in many ways.

Note, however, that "new" doesn't always mean "allocate from the heap". For instance, consider:

DateTime dt = new DateTime(2008, 06, 26);

That calls the DateTime constructor, but doesn't allocate anything on the heap (assuming it's a normal local variable), because DateTime is a value type. In this respect C# is different to Java, as Java doesn't have custom value types, just the primitives.


Thanks Jon - its very clear to me now. tx
.

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