gcc doesn't compile templates

[Michael Schutte]

I am trying to write a wrapper class, which can store any data type to
wrap it into a class. My compiler is gcc (for c++) version 3.3.1 on a
SuSE Linux 9.0 system.
I start with the following code:
template <typename T>
class Wrapper {
public:
Wrapper(T avalue);
private:
int value;
};
in the header wrapper.h, and in wrapper.cpp:
#include "wrapper.h"

template <typename T>
Wrapper<T>::Wrapper(T avalue) {
value = avalue;
}
When I compile now, using
$ gcc -c wrapper.cpp
gcc doesn't report any errors.
Linking with the resulting wrapper.o:
$ gcc -o testwrapper testwrapper.cpp wrapper.o
/tmp/abcdefgh.o(...): In function `main':
undefined reference to Wrapper<int>::Wrapper[in-charge](T)
collect2: ld returned 1 status
What have I done wrong?

 

[Rob Williscroft]

Michael Schutte wrote in @newsreader02.highway.telekom.at in comp.lang.c++:

I am trying to write a wrapper class, which can store any data type to
wrap it into a class. My compiler is gcc (for c++) version 3.3.1 on a
SuSE Linux 9.0 system.
I start with the following code:
template <typename T>
class Wrapper {
public:
Wrapper(T avalue);
private:
int value;
};
in the header wrapper.h, and in wrapper.cpp:
#include "wrapper.h"

Move all the (template) code into your header file

template <typename T>
Wrapper<T>::Wrapper(T avalue) {
value = avalue;
}

You can omit this (if wrapper.cpp is now empty)

When I compile now, using
$ gcc -c wrapper.cpp
gcc doesn't report any errors.
Linking with the resulting wrapper.o:
$ gcc -o testwrapper testwrapper.cpp wrapper.o

Assuming wrapper.cpp is now empty:

$ gcc -o testwrapper testwrapper.cpp


Read the FAQ:

http://www.parashift.com/c++-faq-lite/

It will take a while, but it will be worth it.

HTH.

Rob.

 

[John Harrison]

I am trying to write a wrapper class, which can store any data type to
wrap it into a class. My compiler is gcc (for c++) version 3.3.1 on a
SuSE Linux 9.0 system.
I start with the following code:
template <typename T>
class Wrapper {
public:
Wrapper(T avalue);
private:
int value;
};
in the header wrapper.h, and in wrapper.cpp:
#include "wrapper.h"

template <typename T>
Wrapper<T>::Wrapper(T avalue) {
value = avalue;
}
When I compile now, using
$ gcc -c wrapper.cpp
gcc doesn't report any errors.
Linking with the resulting wrapper.o:
$ gcc -o testwrapper testwrapper.cpp wrapper.o
/tmp/abcdefgh.o(...): In function `main':
undefined reference to Wrapper<int>::Wrapper[in-charge](T)
collect2: ld returned 1 status
What have I done wrong?

Put the template in the header file. Templates belong in header files unless
your compiler supports the export keyword (very few do).

We must get this question about three times a week. It's in the FAQ, its a
good idea to check the FAQ before posting

http://www.parashift.com/c++-faq-lite/containers-and-templates.html#faq-34.14

john

 

[Michael Schutte]

I'm sorry that I haven't checked the FAQs -- I know about the
netiquette. But I mustn't stay long in the WWW (I'm 13 years old and
must use the account of my parents) and have already searched for a long
time...

 

[Aggro]

I'm sorry that I haven't checked the FAQs -- I know about the
netiquette. But I mustn't stay long in the WWW (I'm 13 years old and
must use the account of my parents) and have already searched for a long
time...

Download the faq to your local computer and search off line.

 

[Rakesh Kumar]

Why don't u try using 'g++', instead of gcc.

I am trying to write a wrapper class, which can store any data type to
wrap it into a class. My compiler is gcc (for c++) version 3.3.1 on a
SuSE Linux 9.0 system.
I start with the following code:
template <typename T>
class Wrapper {
public:
Wrapper(T avalue);
private:
int value;
};
in the header wrapper.h, and in wrapper.cpp:
#include "wrapper.h"

template <typename T>
Wrapper<T>::Wrapper(T avalue) {
value = avalue;
}
When I compile now, using
$ gcc -c wrapper.cpp
gcc doesn't report any errors.
Linking with the resulting wrapper.o:
$ gcc -o testwrapper testwrapper.cpp wrapper.o
/tmp/abcdefgh.o(...): In function `main':
undefined reference to Wrapper<int>::Wrapper[in-charge](T)
collect2: ld returned 1 status
What have I done wrong?