Re: Do Variables inside unnamed namespace have Internal Linkage ?
On Fri, 18 Apr 2014 09:00:03 -0700 (PDT)
anand.kulkarni.sg@googlemail.com wrote:
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) ?
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
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