Undefined reference to own files

Question

I have the following Makefile to make my project:

# can be set by the user
LD_FLAGS ?= $(if $(GENERATE_EXECUTABLE),,-shared)
LIBS_FLAGS ?=
INCLUDE_FLAGS ?=
CXX_FLAGS ?= -O3 -Wall -std=c++11

objects = Connector.cpp main.cpp
defines := $(objects:.o=.def)
-include $(defines)
# main target
bin/o.exe: $(objects)
    @echo '[LD] $^ > $@'
    $(CXX) $(LD_FLAGS) $^ -o $@ $(LIBS_FLAGS)

define generate_def
echo '[DEF] $< > $@'
$1 -MM $(INCLUDE_FLAGS) $2 $< > $@
mv -f $@ $@.tmp
sed -e 's|.*:|$@:|' < $@.tmp > $@
sed -e 's/.*://' -e 's/\\$$//' < $@.tmp | fmt -1 | \
    sed -e 's/^ *//' -e 's/$$/:/' >> $@
rm -f $@.tmp
endef
# Compile C++-Files with an appropriate def-file
obj/c++/%.def: %.cpp
    @$(call generate_def,$(CXX),$(CXX_FLAGS))
$(objectscxx): obj/c++/%.o: %.cpp obj/c++/%.def # C++-Files
    @echo '[CXX] $< > $@'
    $(CXX) -c $< $(INCLUDE_FLAGS) $(CXX_FLAGS) -o $@

all: bin/o.exe

main.cpp includes Connector.h and Connector.cpp implements the function declared in Connector.h. Everything compiles fine until the linking stage.

Now when I run it the output is the following:

make all
[DEF] src/main.cpp > obj/c++/src/main.def
[DEF] src/Connector.cpp > obj/c++/src/Connector.def
[CXX] src/Connector.cpp > obj/c++/src/Connector.o
g++ -c src/Connector.cpp -O3 -Wall -g -std=c++11 -o obj/c++/src/Connector.o
[CXX] src/main.cpp > obj/c++/src/main.o
g++ -c src/main.cpp -O3 -Wall -g -std=c++11 -o obj/c++/src/main.o
[LD] obj/c++/src/Connector.o obj/c++/src/main.o obj/res/test.txt.o > bin/o.exe
g++ -static obj/c++/src/Connector.o obj/c++/src/main.o obj/res/test.txt.o -o bin/o.exe 
obj/c++/src/main.o: In function `SpecialConnector::~SpecialConnector()':
C:\Users\Carbon\Documents\Eclipse-Workbench\EpicRPG/src/main.cpp:35: undefined reference to `engine::Connector<SpecialReceiver>::~Connector()'
/**
* More undefined references
*/
obj/c++/src/main.o:C:\Users\Carbon\Documents\Eclipse-Workbench\EpicRPG/src/main.cpp:35: more undefined references to `engine::Connector<SpecialReceiver>::~Connector()' follow
collect2.exe: error: ld returned 1 exit status
make: *** [bin/o.exe] Error 1

Connector.h

/*
 * Connector.h
 *
 *  Created on: 03.06.2014
 *      Author: Carbon
 */

#pragma once
#ifndef CONNECTOR_H_
#define CONNECTOR_H_

#include <type_traits>

namespace engine
{
template<typename DataType, typename ConnectorType>
struct DefaultReceiver {
public:
    DefaultReceiver() {

    }
    virtual ~DefaultReceiver() {

    }

    static const char* receive(DataType data, ConnectorType conn, void* options) {
        return "b";
    }
};

template<template<typename, typename> class Receiver = DefaultReceiver>
class Connector
{
public:
    Connector();
    virtual ~Connector();

    template<typename DataType, typename ConnectorType>
    std::enable_if<true, const char*>::type
    receive(DataType i, ConnectorType c, void* o);
};

} /* namespace engine */
#endif /* CONNECTOR_H_ */

Connector.cpp

/*
 * Connector.cpp
 *
 *  Created on: 03.06.2014
 *      Author: Carbon
 */

#include "Connector.h"

namespace engine
{
template<template<typename, typename> class Receiver>
Connector<Receiver>::Connector()
{
    // TODO Auto-generated constructor stub

}
template<template<typename, typename> class Receiver>
Connector<Receiver>::~Connector()
{
    // TODO Auto-generated destructor stub
}

template<template<typename, typename> class Receiver>
template<typename DataType, typename ConnectorType>
std::enable_if<true, const char*>::type
Connector<Receiver>::receive(DataType input, ConnectorType connector, void* options) {
    return Receiver<DataType, ConnectorType>::receive(input, connector, options);
}
} /* namespace engine */

If you need source-files please comment, I don't think it's necessary (yes, ALL functions etc. are declared, if I include Connector.cpp instead of Connector.h everything is fine).

My specs are: Eclipse M4.3, gcc version 4.8.0

Please show the source and header for engine::Connector – quantdev Jun 03 '14 at 20:24 — quantdev, Jun 03 '14 at 20:24

score 1 · Accepted Answer · edited May 23 '17 at 12:20

1

This compile error is regards to template instantiating. To solve this problem, you can put the implementation of Class Connector into the header file.

This answer gives a very good explanation on the reason, please check it out.

edited May 23 '17 at 12:20

Community

1
1

answered Jun 03 '14 at 20:43

Matt

6,010
25
36

Thanks for the link to the other question. Also the reason why this is the accepted answer. – WorldSEnder Jun 03 '14 at 21:19

score 1 · Answer 2 · answered Jun 03 '14 at 20:43

Most compilers will need the definition of your template Connector in your source file (or alternatively a redeclaration of the template class in the source file)

in particular, the constructor and the destructor should be defined (only declared) in the header file.

In Connector.h :

template<template<typename, typename> class Receiver = DefaultReceiver>
class Connector
{
public:
    Connector() {}
    virtual ~Connector() {}

    template<typename DataType, typename ConnectorType>
    std::enable_if<true, const char*>::type
    receive(DataType i, ConnectorType c, void* o) {}
};

Undefined reference to own files

2 Answers2