Simple question

Hello, i'm developing simple wrapper classes for posix threads and mutexes. Here are the sources

MutexInterface.h

#ifndef MUTEXINTERFACE_H
#define MUTEXINTERFACE_H

class MutexInterface
{
	public:
		virtual void enterMutex() = 0;
		virtual int tryEnterMutex() = 0;
		virtual void leaveMutex() = 0;
	
};

#endif

PosixMutex.h
#ifndef POSIX_MUTEX_H
#define POSIX_MUTEX_H

#include "MutexInterface.h"
#include <pthread.h>

class PosixMutex : public MutexInterface
{
	private:
		pthread_mutex_t *mutex;
	public:
		PosixMutex()
		{
			mutex = new pthread_mutex_t;
		}

		virtual ~PosixMutex()
		{
			delete mutex;
		}
		
		virtual void enterMutex()
		{
			pthread_mutex_lock(mutex);
		}

		virtual int tryEnterMutex()
		{
			return pthread_mutex_trylock(mutex);
		}
		
		virtual void leaveMutex()
		{
			pthread_mutex_unlock(mutex);
		}
};

#endif

ThreadInterface.h
#ifndef THREAD_INTERFACE_H
#define THREAD_INTERFACE_H

class ThreadInterface
{
	public:
		virtual void start() = 0;
};
#endif

<b>PosixThread.h</b>
#ifndef POSIX_THREAD_H
#define POSIX_THREAD_H

#include "ThreadInterface.h"

class PosixThread : public ThreadInterface
{
	private:
	pthread_t *cp_thread;
	void *p_param;
	void *(*fp)(void*);

	public:
	PosixThread(void* lp_param, void *(*routine)(void*))
	{
		cp_thread = new pthread_t;
		p_param = lp_param;
		fp = routine;
	}

	virtual ~PosixThread()
	{
		delete cp_thread;
	}

	virtual void start()
	{
		pthread_create(cp_thread,0,fp, (void*)(p_param));
	}
};

#endif


main.cpp
#include <iostream>
#include <unistd.h>
#include "PosixMutex.h"
#include "PosixThread.h"

PosixMutex mutex;

struct thread {
	int threadID;
};

void *thread_body(void *params);

class LThread : public PosixThread
{
	public:
		LThread(struct thread* ptrData) : PosixThread((void*) ptrData, (void*(*)(void*)) ::thread_body) {}
		void *thread_body(void *params);
		int printThreadAndSleep(thread *data);
		
	private:
};

int LThread::printThreadAndSleep(thread *data) {
	if (!mutex.tryEnterMutex())
	{
		std::cerr << "Succesfully locked by " << data->threadID << std::endl;
	} else {
		std::cerr << "Failed to lock - waiting (" << data->threadID << ")" << std::endl;
		mutex.enterMutex();
	}
	sleep(5);
	std::cerr << "Released by (" << data->threadID << ")" << std::endl;
	mutex.leaveMutex();
}

void *LThread::thread_body(void *params)
{
	thread *data = (thread*) params;
	while (1)
	{
		std::cerr << data->threadID << std::endl;
		printThreadAndSleep(data);
		sleep(2);
	}
}


int main()
{
	pthread_t *cp_thread = new pthread_t;
	struct thread *data;
	for (int i=1;i<6;i++)
	{
		data = new thread;
		data->threadID=i;
		LThread *p=new LThread(data);
		p->start();
	}
	sleep(100);
}

when compiling these sources i'm getting this error:

/var/tmp//cc1V2mOd.o: In function `LThread::LThread[in-charge](thread*)':
/var/tmp//cc1V2mOd.o(.gnu.linkonce.t._ZN7LThreadC1EP6thread+0xa): undefined reference to `thread_body(void*)'
collect2: ld returned 1 exit status

compiler is GCC 3.2

any ideas why it is so?

P.S. I understand that there are a lot of implementations for thread/mutexes classes, but i want this one to become working :)