Hello,
I've run into wieird problem when trying to compile and link our programs with
clang++ on linux instead of g++. It occurs, when:
- template class member definitions are separated from the definition of the
class
- no explicit instantiation is done
- member definitions are available only in some of the units, where the
template is being used.
(Yeah, our code is a mess)
This is simple expamle:
// ----- template.h --------
template< typename T >
struct Template {
Template();
~Template();
};
void doSomething(Template<int>& t);
// ----- template.cpp --------
#include "template.h"
template< typename T >
Template< T >::Template() { }
template< typename T>
Template< T >::~Template() { }
void doSomething(Template<int>& t) {
Template<int> new_t;
t = new_t;
}
// ----- main.cpp --------
#include "template.h"
int main(int argc_, char** argv_) {
Template<int> t;
doSomething(t);
return 0;
}
// ----- end of code
When compiled with clang++:
$ clang++ -o test main.cpp template.cpp
/usr/bin/ld: /tmp/main-e2fa2c.o: in function `main':
main.cpp:(.text+0x2f): undefined reference to `Template<int>::Template()'
/usr/bin/ld: main.cpp:(.text+0x4d): undefined reference to
`Template<int>::~Template()'
/usr/bin/ld: main.cpp:(.text+0x82): undefined reference to
`Template<int>::~Template()'
reading the object files using nm tool shows, the symbol for destructor
instantiated in template.cpp is _ZN8TemplateIiED2Ev, but the main.o requires
symbol _ZN8TemplateIiED1Ev. Notice the difference in one digit: D2 vs D1.
So symbol ...D1... is required, but only ...D2... is available. The D1 version
is generated by clang only for explicit instantiation. g++ generates both D1
and D2 for any type of instantiation.
Can this be considered a bug of clang++? Or does this behaior have some
purpose?
Regards,
JZ
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