Re: question about linker

Bart <bc@freeuk.com> writes:

On 03/12/2024 11:15, Ben Bacarisse wrote:

Bart <bc@freeuk.com> writes:
...

If I write this
>
   int *A, B[10], C(int);
>
My compiler tells me that:
>
   A is a local variable with type 'ref i32' (expressed in other syntax)
   B is a local variable with type '[10]i32'
   C is a function with return type of 'i32', taking one unnamed
     parameter of type 'i32'.
>
(Interestingly, it places C into module scope, so the same declaration can
also create names in different scopes!)

A small correction: that declaration gives all three names the same
scope[1].

>
This is what I observed my compiler doing, because it displays the symbol
table. It puts C into module-scope, so I can access it also from another
function without another declaration (so non-conforming, but I'm long past
caring).

You invented the term "module-scope" and that means you've lost track of
what the scope of a name is in C.  The scope of a name is the portion of
the text program text in which that name can be used to refer the
"thing" that was declared.  Take this example

  // We'll assume that none of the names A, B and C are previously
  // declared here.

  if (...) {
     int *A, B[10], C(int);
     ...
     // The names A, B and C can be used here to refer the things
     // declared (and in the case of A and B defined) above.
     ...
  }
  // None of the names A, B and C can be used here.  The scope ended
  // at the closing brace.

To understand C you need to know what scope is and what linkage is.  C
will have external linkage, because all non-static function declarations
get given external linkage.  That is entirely separate from the scope of
the name being declared.

I can't see gcc's symbol table, but I can't access C from another function
without it having its own declaration, or there being a module-scope one.
>
With gcc, such a declaration inside a function suffices to be able access a
function 'C' defined later in the file.
>

 You are confusing scope with linkage.

>
It's possible. So a function declaration inside a function gives the name
external linkage (?).

Yes.

Which in this context means the function will be outside this one, but
elsewhere in the module, rather than being imported from elsewhere
module.

I can't say yes or no unless you explain all your terms.  C does not
have imports or modules.  A good C book (or the standard) will explain
what external linkage really means.

If I say I find these quirks of C confusing, people will have another go at
me. So let's say it makes perfect sense for 'extern' to mean two different
things!

I don't want to have a go at you, but it seems odd that you don't know
what the scope of a declared name is.  For a compiler writer, that is a
very important concept.

--
Ben.