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From: Janis Papanagnou <janis_papanagnou+ng@hotmail.com>
Newsgroups: comp.lang.c
Subject: Re: Naming conventions (was Re: valgrind leak I can't find)
Date: Sun, 25 Aug 2024 18:55:19 +0200
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On 23.08.2024 17:57, James Kuyper wrote:
>> [...]
> 
> That's possible because C defines separate name spaces of identifiers
> (not to be confused with C++ namespaces) for labels, tags, each struct
> or union type, and attributes; all other identifiers are in the ordinary
> name space. Because of the relevant grammar rules, names in the
> different spaces can never occur in locations where it is ambiguous as
> to which name space the identifier is from. Therefore, C allows you do
> use the same identifier in different name spaces in the same scope with
> different meanings. For example, identifiers in the tag name space are
> always prefixed with struct, union or enum, so they can never be
> confused with names from the ordinary name space.
> 
> In C++, there are separate name spaces only for macros and labels. All
> other identifiers are in the same name space, including tags. Class,
> struct, and union members are not controlled by name spaces, but by
> scope rules that are different from those in C. That's what allows you
> to use a tag without a preceding "class", "struct", or "union" keyword.
> Note: The name space for macros isn't really comparable to the other
> name spaces I've mentioned, which is why C doesn't have such a name
> space. Macros are replaced with their expansions during translation
> phase 3, whereas the other name spaces only become meaningful during
> translation phase 8.
> 
> If C were changed to allow use of tags without "struct" or "union"
> before them, the tag name space would have to be merged into the
> ordinary name space, and that would break all kinds of legacy code that
> uses the same identifier as a tag and as an identifier in the ordinary
> name space. That would be a backwards incompatible change, and the
> committee tends to avoid such changes.

I recall (when I learned C) that the type definitions confused me.

The clear things were ('typedef'-)definitions like

  typedef  struct { double re, im; }  complex;

But then there were also examples like

  typedef  struct tnode {
    ...
    struct tnode * right;
  }  TREENODE, *TREEPTR;

(Both examples taken from an old K&R book.)

In the first case there's no struct name (only the typedef'd one.

In the second case an explicit struct name (necessary for the
type self-reference inside the struct) despite type names being
defined. - Appeared crude to me (and still does).

I don't recall internal name-spaces (as you explain them above)
having been documented and explained. But I may be misremembering.

Janis

> [...]