C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  static inside a namespace? FAQ?          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message nu2beam@yahoo.com Guest Posted: Mon Oct 27, 2003 4:11 pm    Post subject: static inside a namespace? FAQ? Hello! I'm working on an open source project, that shall remain nameless. I've noticed, in the C++ source code, instances where people have defined "static" variables and functions inside a namespace, sometimes an anonymous namespace. namespace Foobar { static long wombat_count; }; Does "static" actually have any value in these contexts? Or is this just some C programmer's misunderstand of namespaces? I searched various FAQs for this question, but didn't find it. If this is in a FAQ somewhere that I missed, a pointer to it would be appreciated. TIA! [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Ben Hutchings Guest Posted: Tue Oct 28, 2003 2:12 am    Post subject: Re: static inside a namespace? FAQ? In article <f1f66b8d.0310262014.130a9778 (AT) posting (DOT) google.com>, [email]nu2beam (AT) yahoo (DOT) com[/email] wrote: Quote: Hello! I'm working on an open source project, that shall remain nameless. I've noticed, in the C++ source code, instances where people have defined "static" variables and functions inside a namespace, sometimes an anonymous namespace. namespace Foobar { static long wombat_count; }; The second semi-colon there is illegal. Quote: Does "static" actually have any value in these contexts? In a named namespace, yes, it gives wombat_count internal linkage, which means among other things that it is distinct from a Foobar::wombat_count declared in any other translation unit. However, given the availability of anonymous namespaces, I don't think are any good reasons to do this. Quote: Or is this just some C programmer's misunderstand of namespaces? Probably. While it's not totally unreasonable in a named namespace, using 'static' at namespace scope in an anonymous namespace is pointless. Quote: I searched various FAQs for this question, but didn't find it. If this is in a FAQ somewhere that I missed, a pointer to it would be appreciated. I don't think this specific case is a FAQ. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Alf P. Steinbach Guest Posted: Tue Oct 28, 2003 2:13 am    Post subject: Re: static inside a namespace? FAQ? On 27 Oct 2003 11:11:55 -0500, [email]nu2beam (AT) yahoo (DOT) com[/email] wrote: Quote: I'm working on an open source project, that shall remain nameless. I've noticed, in the C++ source code, instances where people have defined "static" variables and functions inside a namespace, sometimes an anonymous namespace. namespace Foobar { static long wombat_count; }; Does "static" actually have any value in these contexts? Not in an anonymous namespace. In a named namespace it has the usual (deprecated) meaning, namely to give the item internal linkage so different implementation files can define items of the same name in this namespace. However, linker conflicts can also be avoided by using an anonymous namespace, which in contrast to 'static' allows a function to be used as a template argument. I prefer 'static' because the specification is textually together with the item in question. A purist would have no option but to use an anonymous namespace. Quote: Or is this just some C programmer's misunderstand of namespaces? In an anonymous namespace, yes; in a named namespace, no. Quote: I searched various FAQs for this question, but didn't find it. If this is in a FAQ somewhere that I missed, a pointer to it would be appreciated. AFAIK it's not in the FAQ. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Jeff King Guest Posted: Wed Oct 29, 2003 1:40 am    Post subject: Re: static inside a namespace? FAQ? Alf P. Steinbach <alfps (AT) start (DOT) no> wrote: Quote: Does "static" actually have any value in these contexts? Not in an anonymous namespace. In a named namespace it has the usual (deprecated) meaning, namely to give the item internal linkage so different implementation files can define items of the same name in this namespace. However, linker conflicts can also be avoided by using an anonymous namespace, which in contrast to 'static' allows a function to be used as a template argument. While I mostly agree, your argument neglects other possible uses of static. For example, optimizations might be possible at compile or link time with a static variable that aren't with a global. Such optimizations should be possible with an anonymous namespace, as well, but do current compilers necessarily treat anonymously namespaced variables as static (I can't think of a reason not to, since they should be inaccessible outside the TU). For example, the following code: $ cat foo.cc namespace { int anonymous_variable; } namespace ns { int ns_variable; } static int static_variable; int regular_variable; when compiled with g++ 3.3.2 produces: $ g++ -c foo.cc $ nm foo.o 00000000 B _ZN23_GLOBAL__N_foo.ccEvV75c18anonymous_variableE 00000004 B _ZN2ns11ns_variableE 0000000c B regular_variable 00000008 b static_variable $ nm foo.o | c++filt 00000000 B (anonymous namespace)::anonymous_variable 00000004 B ns::ns_variable 0000000c B regular_variable 00000008 b static_variable Note that the anonymous variable has a unique name, but global linkage. The static variable has local linkage. -Peff [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Bo Persson Guest Posted: Wed Oct 29, 2003 9:31 am    Post subject: Re: static inside a namespace? FAQ? "Alf P. Steinbach" <alfps (AT) start (DOT) no> skrev i meddelandet news:3f9d4546.243695734 (AT) News (DOT) CIS.DFN.DE... Quote: On 27 Oct 2003 11:11:55 -0500, [email]nu2beam (AT) yahoo (DOT) com[/email] wrote: I'm working on an open source project, that shall remain nameless. I've noticed, in the C++ source code, instances where people have defined "static" variables and functions inside a namespace, sometimes an anonymous namespace. namespace Foobar { static long wombat_count; }; Does "static" actually have any value in these contexts? Not in an anonymous namespace. In a named namespace it has the usual (deprecated) meaning, namely to give the item internal linkage so different implementation files can define items of the same name in this namespace. However, linker conflicts can also be avoided by using an anonymous namespace, which in contrast to 'static' allows a function to be used as a template argument. I prefer 'static' because the specification is textually together with the item in question. The you could just write it: namespace { long wombat_count; } Quote: A purist would have no option but to use an anonymous namespace. Right. Bo Persson [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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