Undefined reference while including header in C++

I was working on my project while I decided that I should split it into files. However I got stucked with problem like this and all advice I found via google were about forgetting to link both object files which I am doing right (at least I think so).

Makefile:

test : class.o main.o
 g++ class.o main.o -o test.exe

main.o : main.cpp
 g++ main.cpp -c

class.o : class.cpp
 g++ class.cpp -c

main.cpp

#include <iostream>
#include "class.h"
using namespace std;

int main() {
 Trida * t = new Trida(4);
 t->fce();
 return 0;
}

class.h

#ifndef CLASS
#define CLASS
class Trida {
private:
 int a; 
public:
 Trida(int n); 
 void fce();
};
#endif

class.cpp

#include <iostream>

using namespace std;

class Trida {
private:
 int a;

public:
 Trida(int n) {
  this->a = n;
 } 

 void fce() {
  co开发者_运维问答ut << this->a << endl;
 }
};

Error message:

gwynbleidd@gwynbleidd-pc:~/Skola/test$ make
g++ class.cpp -c
g++ main.cpp -c
g++ class.o main.o -o test.exe
main.o: In function `main':
main.cpp:(.text+0x26): undefined reference to `Trida::Trida(int)'
main.cpp:(.text+0x54): undefined reference to `Trida::fce()'
collect2: ld returned 1 exit status
make: *** [test] Error 1

So here's what you did wrong. In class.cpp you recreate a new Trida class rather than implement the one you've created in class.h. Your class.cpp should look more like this:

#include <iostream>
#include "class.h"

using namespace std;

Trida::Trida(int n)
{
  this->a = n;
}

void Trida::fce() { cout << this->a << endl; }

And really you should be using initialization rather than assignment in your constructor:

Trida::Trida(int n) : a(n) {}

You are defining class trida two times (in the header file class.h and in the source file class.cpp) Your class.cpp file should be like

#include <iostream>
#include "class.h" //include "class.h"
using namespace std;

Trida::Trida(int n):a(n) //Initialization list
{
} 

void Trida::fce()
{
  cout << this->a << endl;
}