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[Samapico]

I have a class (Layer) from which another class (Layer_net) inherits. Other classes will inherit from it eventually.
I made the Layer class a template because there is a specific data type that I want to specify for each child class.
I'm having problems to define class functions outside the class body. They compile fine, but the linker freaks out when one of the function appears in the code.

Code: Show/Hide #define T_LAYER template <typename T> T_LAYER class Layer { public: //stuff... void Func1(); void Func2() { printf("hi, this is Func2\n"); } }; T_LAYER void Layer<T>::Func1() {    printf("hi, this is Func1\n"); } //meanwhile, in another class not far away... struct HeaderNetwork {    char ip[4]; }; class Layer_net : public Layer<HeaderNetwork> { public:    //stuff }; //and in the main... int main(void) {    Layer_net net;    net.Func1();    net.Func2(); }

Ok, it seems the above code works if you put it all in the same file.

I then split it up in a header file and 2 cpp's like so:

header.h

Code: Show/Hide #include <stdio.h> #include <stdlib.h> struct HeaderNetwork {    char ip[4]; }; template <typename T> class Layer { public:    //stuff...    void Func1(int);    void Func2() { printf("hi, this is Func2\n"); } }; //meanwhile, in another class not far away... class Layer_net : public Layer<HeaderNetwork> { public:    //stuff };

layer.cpp

Code: Show/Hide #include <stdio.h> #include <stdlib.h> #include "header.h" template <typename T> void Layer<T>::Func1(int a) {    printf("hi, this is Func1\n"); }

main.cpp

Code: Show/Hide #include "header.h" //and in the main... int main(void) {    Layer_net net;    net.Func1(1);    net.Func2();    getchar(); }

Build results:
1>------ Build started: Project: test, Configuration: Debug Win32 ------
1>Compiling...
1>main.cpp
1>Generating Code...
1>Compiling...
1>layer.cpp
1>Generating Code...
1>Linking...
1>main.obj : error LNK2019: unresolved external symbol "public: void __thiscall Layer<struct HeaderNetwork>::Func1(int)" (?Func1@?$Layer@UHeaderNetwork@@@@QAEXH@Z) referenced in function _main
1>D:\Sam\Prog Projects\GPA785\trunk\Debug\test.exe : fatal error LNK1120: 1 unresolved externals
1>Build log was saved at "file://d:\Sam\Prog Projects\GPA785\trunk\test\Debug\BuildLog.htm"
1>test - 2 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========


Can anyone figure out what's happening?
Using Visual Studio 2005
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[Samapico]

I think I found my answer

http://cpp.developpez.com/faq/cpp/?page=templates#DIVERS_templates
(in french)

Basically, for some reason I have to make the layer.cpp NOT compile, and instead of including the header in it, I must include the cpp at the end of the header file...


I don't really understand why, but it works

[Samapico]

I have another somewhat related problem, and I'm pretty tired now, so excuse me if it's dumb:


Still in my template class, I got some function declared:

DWORD WINAPI threadloop(LPVOID iValue);

and defined later.
And then I want to create a thread in there...

First try:

Code: Show/Hide hthread = CreateThread(NULL, 0, threadloop, "", 0, &threadID);

error C3867: 'Layer<T>::threadloop': function call missing argument list; use '&Layer<T>::threadloop' to create a pointer to member

Ok... second try:

Code: Show/Hide hthread = CreateThread(NULL, 0, &Layer<T>::threadloop, "", 0, &threadID);

error C2664: 'CreateThread' : cannot convert parameter 3 from 'DWORD (__stdcall Layer<T>::* )(LPVOID)' to 'LPTHREAD_START_ROUTINE'

And then I desperately tried to typecast it:

Code: Show/Hide hthread = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)(&Layer<T>::threadloop), "", 0, &threadID);

It failed.
A lot of stuff in there looks weird to me, but I started from an example given by the teacher... but yeah, he wasn't using templates, obviously

[Doc Flabby]

I recommend looking at pthreads or using a C++ framework. Working directly with the Windows API is a PITA but anyways:

Code: Show/Hide hthread = CreateThread(NULL, 0, &Layer<T>::threadloop, "", 0, &threadID);

The problem here is the compiler does not know what T is. Creating an instance of the class Layer<T> and pass it to the function might fix this problem.

eg,

Code: Show/Hide Layer<int> t = new Layer<int>; hthread = CreateThread(NULL, 0, &t::threadloop, "", 0, &threadID);

This might not work btw

I'm not overally familier with templates (i've not used them) in C++ but this link might help http://docs.google.com/gview?a=v&q=cache:twJe98TSVCIJ:www.allankelly.net/static/writing/overload/Threads/ThreadTemplate.pdf+templates+theading&hl=en&gl=uk&sig=AFQjCNEN1kd0XAxuQ2BA4Gq6xtyPrEfVsA[/code]
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[Samapico]

hmmm, the CreateThread call is from the Layer class itself as well, so it should know what T is

Code: Show/Hide T_LAYER void Layer<T>::Start(void) {    if (hthread == NULL)    {       run_thread = true;       hthread = CreateThread(NULL, 0, threadloop, "", 0, &threadID);       } }

Your suggestion doesn't work, I also tried with this->

[Doc Flabby]

You would think it would, but it is C++ after all

I found the source for that link which has threads created inside Templates (go to bottom of the page)

http://www.allankelly.net/writing/softdesign.html
http://www.allankelly.net/static/writing/overload/Threads/threadssource.zip

From the source (snippit) you can see its a bit of a hack job Essentially you have to pass the RunThread an object that implements a "run" function (this might sound familier )

Code: Show/Hide    void RunThread(   T      &x,                long   stackSize = 0)    {       // each object represents one thread       // therefore, should not launch multiple threads with one object       assert (NULL == m_threadHandle);       // other parameters may be dafaulted if needed       DWORD dwStack = (DWORD) stackSize;       // create a  thread       m_threadHandle = CreateThread(                          NULL,         // pointer to thread security attributes                          dwStack,      // initial thread stack size, in bytes                         StartRun,      // pointer to thread function                          &x,            // argument for new thread                         0,            // creation flags                         &m_threadId);   // pointer to returned thread identifier       DWORD last = GetLastError();   // useful for debug stepping       if (NULL == m_threadHandle)       {          throw std::runtime_error("Failed to start thread");       }    } static unsigned long __stdcall StartRun(void *param)    {          T* object = static_cast<T*> (param);   // reclaim object type       object->Run();       return 0;    }

[Samapico]

hmmmm, but the argument of RunThread would still have to be of type Layer<T>, since I want the Run() function to be in there

Not sure how to translate this in my project...

[Dr Brain]

This is why C++ always seems horrible to me. Simple, easy things are complicated and non-intuitive. You use it if you have to, but stay away from it otherwise.
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Smong> so long as 99% deaths feel lame it will always be hyperspace to me

[Samapico]

I could go the easy way and get rid of the template, that would just give me some copy paste to do

[Samapico]