Behavior of the local class

[somenath]

I am not able to understand why the following program does not compile.
#include<iostream>
using namespace std;

template <class T >
void Fun(T t)
{
static int i = t;

class Test {
public:
Test( int t1) {
cout<<"Value = "<<i<<endl;
}
};
Test tt(t);

}


int main(void)
{
Fun<int >(5);
return 0;

}
Whenever I try to compile the program I get the following error
g++ LocalClass.cpp
/tmp/ccfEKvyT.o:LocalClass.cpp:(.text+0x2b): undefined reference to `i'
collect2: ld returned 1 exit status


But I am aware that local class can access the static local variable of enclosing function. The following program proves that as well.

#include<iostream>
using namespace std;

void Fun(int t)
{
static int i=t;

class Test {
public:
Test( int t1) {
cout<<"Value = "<<i<<endl;
}
};
Test tt(t);

}

int main(void)
{
Fun(5);
return 0;

}
This code compile fine. Then what is going wrong with template version of the program?

[Victor Bazarov]

On 1/2/2014 4:22 AM, somenath wrote:
> I am not able to understand why the following program does not compile.
> #include<iostream>
> using namespace std;
>
> template <class T >
> void Fun(T t)
> {
> static int i = t;
>
> class Test {
> public:
> Test( int t1) {
> cout<<"Value = "<<i<<endl;
> }
> };
> Test tt(t);
>
> }
>
>
> int main(void)
> {
> Fun<int >(5);
> return 0;
>
> }
> Whenever I try to compile the program I get the following error
> g++ LocalClass.cpp
> /tmp/ccfEKvyT.o:LocalClass.cpp:(.text+0x2b): undefined reference to `i'
> collect2: ld returned 1 exit status

You must be using a buggy version of the compiler/linker. It compiles
and links (and runs) just fine with VC++ 2012.

> [..]

V
--
I do not respond to top-posted replies, please don't ask

[Alf P. Steinbach]

On 02.01.2014 10:22, somenath wrote:
> I am not able to understand why the following program does not compile.
> #include<iostream>
> using namespace std;
>
> template <class T >
> void Fun(T t)
> {
> static int i = t;
>
> class Test {
> public:
> Test( int t1) {
> cout<<"Value = "<<i<<endl;
> }
> };
> Test tt(t);
>
> }
>
>
> int main(void)
> {
> Fun<int >(5);
> return 0;
>
> }
> Whenever I try to compile the program I get the following error
> g++ LocalClass.cpp
> /tmp/ccfEKvyT.o:LocalClass.cpp:(.text+0x2b): undefined reference to `i'
> collect2: ld returned 1 exit status

This is known g++ bug, already reported at

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52688

As a workaround you can pass the referenced static variable as an
argument, or maybe move it inside the class, or ...


Cheers & hth.,

- Alf

[K. Frank]

Hi somenath (and Alf and Victor)!

On Thursday, January 2, 2014 10:15:57 AM UTC-5, Alf P. Steinbach wrote:
> On 02.01.2014 10:22, somenath wrote:
> > I am not able to understand why the following program does not compile.

> > ...

> > Whenever I try to compile the program I get the following error
> > g++ LocalClass.cpp
> > /tmp/ccfEKvyT.o:LocalClass.cpp:(.text+0x2b): undefined reference to `i'
> > collect2: ld returned 1 exit status
>
> This is known g++ bug, already reported at
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52688
> As a workaround you can pass the referenced static variable as an
> argument, or maybe move it inside the class, or ...
>
> Cheers & hth.,
> - Alf

I tried this with my copy of g++.

For what it's worth, your code compiles and runs fine
when I compile it with a mingw-w64 version of g++:

C:\>g++ --version
g++ (rubenvb-4.8-stdthread) 4.8.1 20130324 (prerelease)


Happy New Year Hacking!


K. Frank