c++ - Include .cpp file?

I've
been trying around with C++ recently.
At the moment I'm trying to program
something I'm sure everone has done at least once: A simple LinkedList
class.
The code is done, but I'm somehow failing to compile it. I've been
googling and it seems like I'm linking the object files wrong. That's what my code
basically looks
like:

test.cpp

#include
            "linkedlist.h"

int main()
{

            LinkedList list;
 // do
            something
}

linkedlist.h

template
            
class LinkedList
{
 // a lot of
            function and variable
            definitions
}

Then
there's a .cpp file called linkedlist.cpp which contains all the actual code of the
LinkerList class. When trying to compile test.cpp using the following
command:

g++
            ..\src\test.cpp

I'm
getting told that there's an undefined reference to 'LinkedList::LinkedList()'. So I've
been thinking that it's being linked wrong as there's more than one .cpp file, so I
tried it like this:

g++ -c -Wall
            -O2 ..\src\test.cpp
g++ -c -Wall -O2 ..\src\linkedlist.cpp
g++ -s
            test.o
            linkedlist.o

However,
this doesn't change anything. The error messages stay the same.
I've been
trying to find some information on the internet, however, it didn't really work
out.

Answer

You're creating a class template, which has
the important caveat that all variable definitions must be placed in the header file so
that they're accessible to all translation units during
compilation.

The reason is the way that
templates work. During compilation, the compiler instantiates template classes based on
your class template definition. It isn't enough for it to have access to only the
declarations or signatures: it needs to have the entire definition
available.

Move all of your method definitions
out of the .cpp file and into the .h
file, and everything should be fine (assuming that you have, in fact, provided a
definition for the default
constructor!).

Alternatively, you
might be able to get around this by explicitly telling your compiler to instantiate the
appropriate template class using something like template class
LinkedList, but this really isn't necessary in such a simple
case. The primary advantage of this over including all of the definitions in the header
file is that it potentially reduces code bloat and speeds up compilation. But it might
not be necessary at all, as compilers have gotten a lot smarter at applying appropriate
optimizations.