   Header files
  Hello,I am trying to learn how to use header files but am having trouble.  Here is what I have:main.cpp#include <iostream>#include "func1.h"using namespace std;int main(){cout << "This is main.cpp" << endl;func1();return 0;}func1.cpp#include "func1.h"#include <iostream>using namespace std;void func1(){cout << "This is func1." << endl;}func1.h#ifndef __FUNC1_H_#define __FUNC1_H_void func1();#endifI get the following error:g++ -o headers main.o -lpthreadmain.o: In function `main':main.cpp:(.text+0x83): undefined reference to `func1()'collect2: ld returned 1 exit statusmake: *** [headers] Error 1I am not sure what I am doing wrong.  Thanks.   
  You're only linking main.o not func1.o.   ;  Ok. Thanks, I missed that.   