Re: [Tinycc-devel] defined twice error commented out

[grischka]

Michael Matz wrote:
> ... In C it's not 
> allowed to have two definitions of the same non-static symbol, simple as 
> that.  It's not only for when initialized with different values or the 
> like; it's undefined no matter what.

Maybe it isn't that clear.  See below from the c99 draft, in particular
the word "tentative".

Anyway, it's not that TCC's behavior in that area couldn't be better.
Whether or not -f(no-)common should make a difference may be arguable
too.

-- gr


> 6.9.2 External object definitions
>
> Semantics
>
> 1 If the declaration of an identifier for an object has file scope
>   and an initializer, the declaration is an external definition for
>   the identifier.
>
> 2 A declaration of an identifier for an object that has file scope
>   without an initializer, and without a storage-class specifier or
>   with the storage-class specifier static, constitutes a tentative
>   definition. If a translation unit contains one or more tentative
>   definitions for an identifier, and the translation unit contains
>   no external definition for that identifier, then the behavior is
>   exactly as if the translation unit contains a file scope declaration
>   of that identifier, with the composite type as of the end of the
>   translation unit, with an initializer equal to 0.
>
> 3 If the declaration of an identifier for an object is a tentative
>   definition and has internal linkage, the declared type shall not
>   be an incomplete type.
>
> 4 EXAMPLE 1
>
> int i1 = 1;         // definition, external linkage
> static int i2 = 2;  // definition, internal linkage
> extern int i3 = 3;  // definition, external linkage
> int i4;             // tentative definition, external linkage
> static int i5;      // tentative definition, internal linkage
>
> int i1; // valid tentative definition, refers to previous
> int i2; // 6.2.2 renders undefined, linkage disagreement
> int i3; // valid tentative definition, refers to previous
> int i4; // valid tentative definition, refers to previous
> int i5; // 6.2.2 renders undefined, linkage disagreement
>
> extern int i1; // refers to previous, whose linkage is external
> extern int i2; // refers to previous, whose linkage is internal
> extern int i3; // refers to previous, whose linkage is external
> extern int i4; // refers to previous, whose linkage is external
> extern int i5; // refers to previous, whose linkage is internal
>
> 5 EXAMPLE 2
>
> If at the end of the translation unit containing
>     int i[];
> the array i still has incomplete type, the implicit initializer causes
> it to have one element, which is set to zero on program startup.