Re: OS/2 Patches (4)

[Bruno Haible]

Andreas Buening wrote:
> > > it's still a bad idea not to initializes global variables.
> > 
> > Crap.  Learn the difference between the bss and data sections.
> 
> unfortunately, I know that this (to use your words)
> crap is Standard C. It's unbelievable, but true.

Please read the standards before complaining about them. Quoting
ISO/IEC 9899:1999 (a.k.a. ISO C 99) section 6.7.8 paragraph 10:

    If an object that has automatic storage duration is not initialized
    explicitly, its value is indeterminate. If an object that has static
    storage duration is not initialized explicitly, then:
    - if it has pointer type, it is initialized to a null pointer;
    - if it has arithmetic type, it is initialized to (positive or
      unsigned) zero;
    - if it is an aggregate, every member is initialized (recursively)
      according to these rules;
    - if it is a union, the first named member is initialized (recursively)
      according to these rules.

and section 6.2.4 paragraph 3:

    An object whose identifier is declared with external or internal
    linkage, or with the storage-class specifier static has static storage
    duration. Its lifetime is the entire execution of the program and its
    stored value is initialized only once, prior to program startup.

> As well as "Different
> names with external linkage must differ (other than in case)
> within the first six characters".

This also is an urban legend. In ISO C 99 the first 255 characters
(at least) are significant. And of course 'x' and 'X' are different
names. This is C, not Pascal or Fortran.

> Ah, you're asking why I think this is a bad idea? A good
> question. These so called "tentative definitions" are a very
> funny feature. You can define as many variables of an arbitrary
> type with the same name, one in each source file. Cool, isn't
> it? This results in a so called "common" variable because
> all these variables share the same address. Why is this a
> bad programming style? ...

Most people agree that using the "common" variables feature of
Unix linkers is bad, because it's unportable. But this doesn't
make implicitly initialized (= BSS allocated) variables a bad
feature.

Similarly: Division by zero is bad, but that doesn't make the
use of division bad by itself. You just have to be careful when you
use it.

Bruno