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From: Goran on 2 Jul 2010 06:23
On Jul 1, 4:54 pm, "Martin B." <0xCDCDC...(a)gmx.at> wrote:
> Is an anonymous / unnamed namespace unique to the translation unit or is
> it simply unique, that is, is the following legal:
>
> *** file.cpp ***
> // ...
> namespace {
> int HelperFn(double d);};
>
> // ...
> void ExternalFn() {
> // ...
> int x = HelperFn(1.0);
> // ...}
>
> // ...
> namespace { // Is this the *same* anonymous namespace as above?
> int HelperFn(double d) {
> // ...
> return l;
> }};
>
> *** ***
>
> It works on VC++2005 but is it std behaviour?

Dunno about a standard, but e.g. GCC 3.4.5, MS ccompiler from VS 2008
and comeau online don't like it. HelperFn is a doubly-defined symbol
for all three.

Bug in VC2005?

Goran.


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From: Ric Parkin on 2 Jul 2010 09:05
On 1 July, 15:54, "Martin B." <0xCDCDC...(a)gmx.at> wrote:
> Is an anonymous / unnamed namespace unique to the translation unit or is
> it simply unique, that is, is the following legal:
>
> *** file.cpp ***
> // ...
> namespace {
> int HelperFn(double d);};
> }
> namespace { // Is this the *same* anonymous namespace as above?
> int HelperFn(double d) {
> // ...
> return l;
> }};
> It works on VC++2005 but is it std behaviour?

Yes, each translation unit has a single unnamed namespace, unique to
that TU

See 7.3.1.1 where it says it's equiv to

namespace unique {}
using namespace unique;
namespace unique { ... }

where all uses of unique in a translation unit are replaced by the
same identifier, and this identifier differes from all others in the
entire programme.

ie even though uses the term "unnamed" the standard actually says it
has a name, it's just that you don't know what it is so can't use it.

Ric

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From: CornedBee on 2 Jul 2010 09:05
On Jul 1, 4:54 pm, "Martin B." <0xCDCDC...(a)gmx.at> wrote:
> Is an anonymous / unnamed namespace unique to the translation unit or is
> it simply unique

Unique to the translation unit, see [namespace.unnamed]p1:
"all occurrences of unique in a translation unit are replaced by the
same identifier, and this identifier differs from all other
identifiers in the entire program"

Sebastian


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From: Nick Hounsome on 3 Jul 2010 07:55
On 2 July, 21:54, Daniel Kr�gler <daniel.krueg...(a)googlemail.com>
wrote:
> On 1 Jul., 16:54, "Martin B." <0xCDCDC...(a)gmx.at> wrote:

> > *** file.cpp ***
> > // ...
> > namespace {
> > int HelperFn(double d);};
>
> > // ...
> > void ExternalFn() {
> > // ...
> > int x = HelperFn(1.0);
> > // ...}
>
> > // ...
> > namespace { // Is this the *same* anonymous namespace as above?
> > int HelperFn(double d) {
> > // ...
> > return l;
> > }};

> The C++ standard guarantees that *all* occurences
> of the same unnamed namespace within the same
> translation unit do have the same identifier, see
> C++03, 7.3.1.1 [namespace.unnamed]/1:

I knew this but it had never occurred to me to use it to forward
declare local functions so that I could put the definitions at the end
of the file after the more important public stuff. I've been using
static for that all these years. Doh!


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From: Francis Glassborow on 3 Jul 2010 17:40
Ric Parkin wrote:
> On 1 July, 15:54, "Martin B." <0xCDCDC...(a)gmx.at> wrote:
>> Is an anonymous / unnamed namespace unique to the translation unit or is
>> it simply unique, that is, is the following legal:
>>
>> *** file.cpp ***
>> // ...
>> namespace {
>> int HelperFn(double d);};
>> }
>> namespace { // Is this the *same* anonymous namespace as above?
>> int HelperFn(double d) {
>> // ...
>> return l;
>> }};
>> It works on VC++2005 but is it std behaviour?
>
> Yes, each translation unit has a single unnamed namespace, unique to
> that TU
>
> See 7.3.1.1 where it says it's equiv to
>
> namespace unique {}
> using namespace unique;
> namespace unique { ... }
>
> where all uses of unique in a translation unit are replaced by the
> same identifier, and this identifier differes from all others in the
> entire programme.

Well that is the intention though I am not sure how an implementer can
guarantee it. Yes we can make it very unlikely that a generated unique
identifier is not actually unique but it is not proof against
Machiavelli. (generate an object file, clone it by another name and then
link both files into the same executable.)

>
> ie even though uses the term "unnamed" the standard actually says it
> has a name, it's just that you don't know what it is so can't use it.

Yes, I first came across the concept in Forth. There has to be a name
but it is unutterable (by the programmer). Actually Forth had a really
unutterable name that it used for vocabulary roots, ' ' (i.e. a space)
which was impossible for the programmer to utter from the keyboard
(whitespace has no significance outside the inner workings of the
implementation). Unfortunately C++ cannot be quite so clever because the
names have to be readable by the linker.

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