Do Variables inside unnamed namespace have Internal Linkage ?

[anand.ku...@googlemail.com]

I have below code snippet.


--- CODE START ------

#include<iostream>

namespace {

int p;

}

static int i;

template<const int& T> struct Sample { };


using namespace std;

int main(int argc,char* argv[]) {

Sample<p> o1; // works although internal linkage as per c++ reference.

Sample<i> o2; // error because static variable has internal linkage and
Template argument initialization requires external linkage.


}

--- CODE END ------

ibm c++ reference says that unnamed namespace variables have internal
linkage hence better to use than static variables. - (A)
http://publib.boulder.ibm.com/infocenter/comphelp/v8v101/index.jsp?topic=%2F
com.ibm.xlcpp8a.doc%2Flanguage%2Fref%2Funnamed_namespaces.htm

also i verified via g++ as well as Microsoft compiler that "template
arguments cannot be names with internal linkage" - (B)
( also verified via below link )
http://www.comeaucomputing.com/techtalk/#nostatic

so if above code does not work Which of above statements is incorrect (A) or
(B) ?


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[Chris Vine]

In C++89/03, template type arguments cannot have internal linkage and
the anonymous namespace has external linkage. In C++11, template type
arguments can have internal linkage and the anonymous namespace has
internal linkage.

The change in linkage is most likely to affect code using functions
declared with C linkage, say for interfacing with C libraries. Putting
these in anonymous namespace in C++98/03 was useless (it didn't name
mangle functions with C linkage and it didn't limit linking to the
particular translation unit either). In C++11 however declaring a
function with anonymous namespace has a similar effect to using the
static keyword.

Chris