Question

I’ve got a C++ template class split into two files using #include directive as suggested in this link –> Templates spread across multiple files

For both files I’ve used the standard naming *.h and *.cpp.
In the makefile I’ve included the *.h one since – as I understand it – both files split in such way are in fact one from the compiler point of view. I’ve set the same compilation options as in case of compiling a ususal *.cpp file.

However, when I try to compile it through makefile i get the following error:

Stos.o: file not recognized: File format not recognized
collect2: ld returned 1 exit status
make: *** [program] Error 1

I’ve read somewhere that it might be due to the fact that I compile *.h file. I do not know what should I do instead.

Thank you for your help.

EDIT

I am posting the makefile itself to make matter more clear. Please, excuse me that the names are not in English, however in this case this shouldn’t be a problem. I’ve updated the error message so that it fits the makefile.

Because of suggestions here, I’ve already changed names for template files from *.h and *.cpp mentioned above to *.hpp and *.tpp.

CC=g++
CFLAGS=-c -Wall -pedantic -W
COMP= $(CC) $(CFLAGS)

program: Graf.o wgraf.o wnazwe.o menu.o Stos.o TabDyn.o komunikaty.o main.o
    $(CC) Graf.o wgraf.o wnazwe.o menu.o Stos.o TabDyn.o komunikaty.o main.o -o program
Graf.o: graf_struktura/Graf.cpp graf_struktura/Graf.h lifo/TabDyn.hpp lifo/Stos.hpp
    $(COMP) graf_struktura/Graf.cpp -o $@
wgraf.o: wczytywanie_grafu/wczytaj_graf.cpp wczytywanie_grafu/wczytaj_graf.h    graf_struktura/Graf.h lifo/Stos.hpp
    $(COMP) wczytywanie_grafu/wczytaj_graf.cpp -o $@
wnazwe.o: wczytywanie_grafu/wczytaj_nazwe_pliku.cpp    wczytywanie_grafu/wczytaj_nazwe_pliku.h wczytywanie_grafu/komunikaty.cpp 
    $(COMP) wczytywanie_grafu/wczytaj_nazwe_pliku.cpp -o $@
komunikaty.o: wczytywanie_grafu/komunikaty.cpp
    $(COMP) wczytywanie_grafu/komunikaty.cpp
menu.o: menu/menu.cpp graf_struktura/Graf.h
    $(COMP) menu/menu.cpp
main.o: main.cpp wczytywanie_grafu/wczytaj_nazwe_pliku.h    wczytywanie_grafu/wczytaj_graf.h menu/menu.cpp graf_struktura/Graf.h
    $(COMP) main.cpp
#Here is the issue.
Stos.o: lifo/Stos.hpp lifo/Stos.tpp lifo/TabDyn.hpp
    $(COMP) lifo/Stos.hpp -o $@
TabDyn.o: lifo/TabDyn.hpp lifo/TabDyn.tpp
    $(COMP) lifo/TabDyn.hpp -o $@

Compiler actually creates "Stos.o" but fails to include it in "program" producing quoted error.

Hope that now my issue is more clear. Sorry if makefile is not elegant. I’m still a beginner at makefiles, please be understanding.

Answer 1

If your MyClass.h looks like

#ifndef MYCLASS_H
#define MYCLASS_H
template<typename T>
  struct MyClass
  {
    void f();
  };
#include "MyClass.tcc"
#endif

And the MyClass.tcc file looks like

template<typename T>
  void
  MyClass::f(T)
  { }

Then code that uses the template, say in a file called main.cpp, looks like:

#include "MyClass.h"

int main()
{
  MyClass<int> m;
  m.f(1);
}

And the Makefile could look like:

main: main.o
    $(CXX) $^ $(LDFLAGS) -o $@

main.o: main.cpp MyClass.h MyClass.tcc
    $(CXX) $(CXXFLAGS) $< -o $@

The makefile should not compile the template header, it compiles the main.cpp file into a .o, and lists the headers as dependencies. If either of the headers or main.cpp changes then main.o will be recompiled. Don’t compile the headers though.

FWIW, in my own code I use .cc for source files, .h for headers and .tcc for inline definitions. GCC knows that .tcc is a header file and will treat it correctly (as a header) if you say g++ foo.tcc, see http://gcc.gnu.org/onlinedocs/gcc/Overall-Options.html for the file extensions GCC recognises.

N.B. rather than manually listing all the header dependencies you can use GCC to produce makefile fragments listing the dependencies, e.g. for main.cpp you would generate a main.d and in the makefile do include main.d … that’s beyond the scope of this answer though.