Thread: Undefined reference - however they ARE defined

I'm having an odd problem with my code. I have a template function in my class.
This is in the header file lcmp.h as so:

Code:

class LCMPMsg{
    public:
        ...
        template <class T> T* getField(const char* name);
        ...
};

I then have the implementation of this function in lcmp.cpp ...

Code:

template <class T>
T* LCMPMsg::getField(const char* name){
	LCMPMsgFieldIt i = _findField(name);
	if(i != _fields.end()){
		return (T*)(*i).data;		
	}
	return 0;
}

Yet, I receive undefined reference to <T> at compile time - T being whatever type I've used in the call.. for example:

Code:

if(msg->fieldExists("string")){
    std::cout << "String: " << msg->getField<char>("string") << "\n";
}

So I receive undefined reference to `char* LCMPMessage::getField<char>(char const*)' ... But oddly not a single undefined reference to ANY of the other functions in the lcmp.cpp - including the template setField() function nor _setField() which is also a template function:

Code:

template <typename T>
void LCMPMsg::setField(const char* name, T value){
    int size = sizeof(T);
    _setField(name, reinterpret_cast<const unsigned char*>(&value), size);
}

If I copy the getField() code directly into the file I'm using it in, it works just fine. How can all of the other functions be picked up but my getField() it's quite confusing.

I'm using the GCC compiler... Here's the console dump:

Code:

**** Build of configuration Debug for project gsocket ****

make -k all 
Building file: ../main.cpp
Invoking: GCC C++ Compiler
g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"main.d" -MT"main.d" -o"main.o" "../main.cpp"
Finished building: ../main.cpp
 
Building target: gsocket
Invoking: GCC C++ Linker
g++  -o"gsocket"  ./gsocket.o ./main.o  ./lcmp/lcmp.o   
./main.o: In function `main':
/home/michael/projects/gsocket/Debug/../main.cpp:42: undefined reference to `char* LCMPMsg::getField<char>(char const*)'
/home/michael/projects/gsocket/Debug/../main.cpp:45: undefined reference to `float* LCMPMsg::getField<float>(char const*)'
/home/michael/projects/gsocket/Debug/../main.cpp:48: undefined reference to `double* LCMPMsg::getField<double>(char const*)'
collect2: ld returned 1 exit status
make: *** [gsocket] Error 1
make: Target `all' not remade because of errors.
Build complete for project gsocket

Actually I have rewritten it to return const T&, because it avoids problems in tracking data size of elements stored internally for one.

Thanks for the heads up on the potential IDE problems - I like that idea so I'll probably go with that, seems somewhat more elegant.