I've taken a look at your previous posts and indeed... So, OP, you'll have to learn about a pretty dumb feature of C (that has nothing to do with XS per se). There is a difference between

typedef struct Foo {
   ...
} Foo;
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and

typedef struct {
    ...
} Foo;
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In the first case, you can use struct Foo and Foo interchangeably. I think... Compatibility rules for types in C are pretty complex and obscure. Anyway, in the second case you don't have struct Foo, you have just Foo which is a name for an anonymous struct (while Foo in struct Foo is not a name but a tag). Yes, it's pretty confusing... but don't worry: there are some things in C that are a lot more obscure and error prone than that :) I suggest you to avoid typedefs for the time being.