• mina86@lemmy.wtfEnglish
    46·
    2 days ago

    This is hardly newsworthy. If the extensions were called ‘Jabberwocky C Extennsions’ no one would have cared. The extension allows for tagged unnamed structs inside of a struct, e.g.:

    struct inner { /* ... */ };
struct outer {
    int value;
    struct inner;
};
      • mina86@lemmy.wtfEnglish
        13·
        2 days ago

        Tag is what goes after the struct keyword to allow referring to the struct type. Structs don’t have to have a tag. Name is what field are called. Adapting Obin’s example:

        struct foo { int baz; };
struct bar { struct foo qux; };
struct bar data;
data.qux.baz = 0;

        foo and bar are tags for struct foo and struct bar types respectively; baz and qux are field names; and data is a variable name.

      • Obin@feddit.org
        20·
        2 days ago

        You mean ‘unnamed’ is what’s confusing you?

        Normally you can do anonymous struct/union members or struct struct/union members that are tagged structs but not anonymous.

        I.e. in standard C you’d have to do either:

        struct foo { int baz; };
struct bar { struct foo foo; };
...
struct bar data;
data.foo.baz = 0;

        or:

        struct bar { struct {  int baz; } foo; };
...
struct bar data;
data.baz = 0;

        but to do the following, you’d need the extension:

        struct foo { int baz; };
struct bar { struct foo; };
...
struct bar data;
data.baz = 0;
        • mina86@lemmy.wtfEnglish
          8·
          1 day ago

          Minor correction: Unnamed structs and unions (so your second example) are not part of C. They are GNU extensions.

          • MinekPo1 [it/she]@lemmygrad.ml
            3·
            2 days ago

            “ANSI C” by Kernighan and Ritchie disagrees , including that syntax (note : retranslation from Polish as that’s the language my copy is in) :

            A8.3

            […]

            struct-union-specifier:
            , union-struct identifier ₒₚₜ { compound-declaration-list }
            , union-struct identifier

            […]

            Specifiers of structures or unions with [a compound declaration] list, but with no label [identifier], creates a unique type; it may only be referred to in the declaration in which it is part.

            • mina86@lemmy.wtfEnglish
              1·
              1 day ago

              Yes, but I was talking about field name, not struct tag. And up to C99 my comment was correct.