• Richard <Richard_member pathlink.com> Jan 23 2003
• "Walter" <walter digitalmars.com> Jan 23 2003
• Richard Grant <fractal clark.net> Jan 24 2003
• "Walter" <walter digitalmars.com> Jan 24 2003
• Richard Grant <fractal clark.net> Feb 28 2003
• "Walter" <walter digitalmars.com> Feb 28 2003
• %u Souveek Kumar Bose <imsouveek gmail.com> Feb 20 2007

Richard <Richard_member pathlink.com> writes:

2.1 and 2.1-8

Problem: template declaration in one source file (.h), template member function
definitions in another source file (unit A), and template member function use in
a third source file (unit B). Linker complains that symbol for template member
function is undefined.

// test.h
template <class T>
struct A {
void fn();
};

// test.cpp
#include "test.h"
template <class T> void A<T>::fn() { }

// main.cpp
#include "test.h"
void main() {
A<int> a;
a.fn();
}

// Error 42: Symbol Undefined
// ?fn ?$A H  QAEXXZ (void syscall A<int >::fn(void ))

This has slowly become a high priority for me.

Richard

"Walter" <walter digitalmars.com> writes:

Unfortunately, you'll need to put the template bodies into the header files.
That's the way it is with a separate compilation model. The good part is
that there's no penalty for doing so (other than a bit slower compilation
speed).

"Richard" <Richard_member pathlink.com> wrote in message
news:b0pm9c$3p1$1 digitaldaemon.com...
 2.1 and 2.1-8

 Problem: template declaration in one source file (.h), template member


 definitions in another source file (unit A), and template member function


 a third source file (unit B). Linker complains that symbol for template


 function is undefined.

 // test.h
 template <class T>
 struct A {
 void fn();
 };

 // test.cpp
 #include "test.h"
 template <class T> void A<T>::fn() { }

 // main.cpp
 #include "test.h"
 void main() {
 A<int> a;
 a.fn();
 }

 // Error 42: Symbol Undefined
 // ?fn ?$A H  QAEXXZ (void syscall A<int >::fn(void ))

 This has slowly become a high priority for me.

 Richard

Richard Grant <fractal clark.net> writes:

In article <b0ptcq$8f3$1 digitaldaemon.com>, Walter says...
Unfortunately, you'll need to put the template bodies into the header files.
That's the way it is with a separate compilation model. The good part is
that there's no penalty for doing so (other than a bit slower compilation
speed).


Ok, that's fine for me, and a non exhaustive search of boost lib code indicates
awareness of compilation models, but it does create problems with libs that are
unaware.. just to be clear: are you saying that this behavior is by design, and
that no change is anticipated?

Richard

"Walter" <walter digitalmars.com> writes:

"Richard Grant" <fractal clark.net> wrote in message
news:b0r5gj$t14$1 digitaldaemon.com...
 In article <b0ptcq$8f3$1 digitaldaemon.com>, Walter says...
Unfortunately, you'll need to put the template bodies into the header




That's the way it is with a separate compilation model. The good part is
that there's no penalty for doing so (other than a bit slower compilation
speed).




 awareness of compilation models, but it does create problems with libs


 unaware.. just to be clear: are you saying that this behavior is by


 that no change is anticipated?


Yes. I also don't think you'll find any code otherwise. I think all the
existing compilers work that way.

Richard Grant <fractal clark.net> writes:

In article <b0rq1h$17o7$1 digitaldaemon.com>, Walter says...

Yes. I also don't think you'll find any code otherwise. I think all the
existing compilers work that way.


In some other thread on Template definitions in different translation units, we
were talking about irrelevant details. According to 14-7 of the template
introduction, The export keyword handles this issue. But this does not work:

export template <class T> struct A {
// Error: missing decl-specifier-seq for declaration of 'export'
void fn();
};

template <class T> void A<T>::fn() { }

int main() {
A<int> a;
a.fn();
}

Richard

"Walter" <walter digitalmars.com> writes:

Exported templates do not work yet.

"Richard Grant" <fractal clark.net> wrote in message
news:b3ngi1$2jmr$1 digitaldaemon.com...
 In article <b0rq1h$17o7$1 digitaldaemon.com>, Walter says...

Yes. I also don't think you'll find any code otherwise. I think all the
existing compilers work that way.


 In some other thread on Template definitions in different translation


 were talking about irrelevant details. According to 14-7 of the template
 introduction, The export keyword handles this issue. But this does not


 export template <class T> struct A {
 // Error: missing decl-specifier-seq for declaration of 'export'
 void fn();
 };

 template <class T> void A<T>::fn() { }

 int main() {
 A<int> a;
 a.fn();
 }

 Richard

%u Souveek Kumar Bose <imsouveek gmail.com> writes:

For template function declarations and definitions to be in
different files, the declarations must be available in the file in
which they are defined. That is whats the root of all problems in
this case

For template class/function definitions to be in one file and
their declarations in another, you can use one of 2 methods:-

In the file test.h, add #include "test.cpp" after the template
struct definition

Use the export keyword in test.cpp as follows:-
export template<class T> void A<T>::fn() {}
However, most compilers dont support the keyword export. So, you
can do one of two things...
1> Follow method one above
2> Keep template function/struct/class declarations and
definitions in the same file.