Which compiler flag ???

[Rajiv Guliani <rajiv dot guliani at oracle dot com>]

Which compiler flag should be use???

I am using Redhat-Linux version 2.91.66

$ g++ -v
Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/egcs-/specs
gcc version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)
 

I am getting multiple "definition error" in templates while linking all the ".o" file when i didn't use any flag.

I tried with -frpo flag but the compiler keeps on recompiling 2 or 3 files and was not able to make the shared objects.

Then i tried with -fexternal-templates, i am getting "undefined symbols" in templates while making the executables.
 
 

Now, I am checking with these three test programs.
 

// template.h

template <class T>
class TAnyClass
{
private:
        T data;
public:
        TAnyClass(const T arg) : data(arg) {};
        const T & GetData() const;
};

template <class T>
TAnyClass<T> * MakeObject(const T param);
 
 
 
 

// template.cpp

#include "template.h"
#include <string>

template <class T>
const T & TAnyClass<T>::GetData() const
{
        return data;
}

template <class T>
TAnyClass<T> * MakeObject(const T param)
{
        return new TAnyClass<T>(param);
}

/*
template class TAnyClass<int>;
template class TAnyClass<double>;
template class TAnyClass<string>;
template TAnyClass<string> * MakeObject(const string param);
*/
 
 
 

// usetemplate.cpp

#include <iostream.h>
include <string>
#include "template.h"

/*
extern template class TAnyClass<int>;
extern template class TAnyClass<double>;
extern template class TAnyClass<string>;
extern template class TAnyClass<string> * MakeObject(string param);
*/

int main()
{
        TAnyClass<int> obj1(123);
        cout << obj1.GetData() << endl;

        TAnyClass<double> obj2(3.14159);
        cout << obj2.GetData() << endl;

        TAnyClass<string> obj3("Hello");
        cout << obj3.GetData() << endl;

        string s("World");
        TAnyClass<string> *p = MakeObject(s);
        cout << p->GetData() << endl;
        delete p;
 
        return 0;
}
 
 

$ g++ -c template.cpp
$ g++ usetemplate.cpp template.o
/tmp/cc54vWyK.o: In function `main':
/tmp/cc54vWyK.o(.text+0xd): undefined reference to `TAnyClass<int>::TAnyClass(int)'
/tmp/cc54vWyK.o(.text+0x1e): undefined reference to `TAnyClass<int>::GetData(void) const'
/tmp/cc54vWyK.o(.text+0x51): undefined reference to `TAnyClass<double>::TAnyClass(double)'
/tmp/cc54vWyK.o(.text+0x62): undefined reference to `TAnyClass<double>::GetData(void) const'
/tmp/cc54vWyK.o(.text+0xa7): undefined reference to `TAnyClass<basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> > >::TAnyClass(basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> >)'
/tmp/cc54vWyK.o(.text+0xb8): undefined reference to `TAnyClass<basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> > >::GetData(void) const'
/tmp/cc54vWyK.o(.text+0x102): undefined reference to `TAnyClass<basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> > > * MakeObject<basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> > >(basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> >)'
/tmp/cc54vWyK.o(.text+0x118): undefined reference to `TAnyClass<basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> > >::GetData(void) const'
collect2: ld returned 1 exit status
 
 

$ g++ -c -frepo template.cpp
$ g++ -c -frepo usetemplate.cpp
$ g++ usetemplate.o template.o
usetemplate.o: In function `main':
usetemplate.o(.text+0x1e): undefined reference to `TAnyClass<int>::GetData(void) const'
usetemplate.o(.text+0x62): undefined reference to `TAnyClass<double>::GetData(void) const'
usetemplate.o(.text+0xb8): undefined reference to `TAnyClass<basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> > >::GetData(void) const'
usetemplate.o(.text+0x102): undefined reference to `TAnyClass<basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> > > * MakeObject<basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> > >(basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> >)'
usetemplate.o(.text+0x118): undefined reference to `TAnyClass<basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> > >::GetData(void) const'
collect2: ld returned 1 exit status
 
 

$ g++ -c -fexternal-templates template.cpp
$ g++ -c -fexternal-templates usetemplate.cpp
template.h: In instantiation of `TAnyClass<int>::TAnyClass<int>(int)':
usetemplate.cpp:14:   instantiated from here
template.h:10: warning: template `TAnyClass<T>::TAnyClass(T)' defined in file without #pragma interface
$ g++ usetemplate.o template.o
usetemplate.o: In function `main':
usetemplate.o(.text+0x1e): undefined reference to `TAnyClass<int>::GetData(void) const'
usetemplate.o(.text+0x62): undefined reference to `TAnyClass<double>::GetData(void) const'
usetemplate.o(.text+0xb8): undefined reference to `TAnyClass<basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> > >::GetData(void) const'
usetemplate.o(.text+0x102): undefined reference to `TAnyClass<basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> > > * MakeObject<basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> > >(basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> >)'
usetemplate.o(.text+0x118): undefined reference to `TAnyClass<basic_string<char, string_char_traits<char>, __default_alloc_template<1, 0> > >::GetData(void) const'
collect2: ld returned 1 exit status
 
 

The problem of this solution is to have template instantiation in template.cpp and to use extern declaration in usetemplate.cpp. I have commented those lines.
But we are using third party tool "ospace". We can't change in ospace cpp files.

Can any one have the solution for this????

Rajiv Guliani.