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C # - Why do I need to initialize the [Out] parameter

I have several methods imported from native.dll using the following syntax:

internal static class DllClass {
    [DllImport("Example.dll", EntryPoint = "ExampleFunction")]
    public static extern int ExampleFunction([Out] ExampleStruct param);
}

Now, since I indicated paramhow [Out], I would expect at least one of the following snippets to be valid:

ExampleStruct s;
DllCass.ExampleFunction(s);

ExampleStruct s;
DllCass.ExampleFunction([Out] s);

ExampleStruct s;
DllCass.ExampleFunction(out s);

However, none of them work. The only way I worked with is to initialize s.

ExampleStruct s = new ExampleStruct();
DllCass.ExampleFunction(s);

I managed to fix this by rewriting the first code snippet to the following code, but that seems redundant.

internal static class DllClass {
    [DllImport("Example.dll", EntryPoint = "ExampleFunction")]
    public static extern int ExampleFunction([Out] out ExampleClass param);
}

I read. What is the difference between [Out] and out in C #? And because the accepted answer says that [Out]and outare equivalent in the context, he left me puzzled why it did not work for me, and if my "solution" approach.

? out? [Out]?

+4
2

OutAttribute runtime, . out , .

out , OutAttribute . . .

+2

? , : out , .

0

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