Not possible to compile. Headers files.Enclosed own objects definition - c++

Question

Here I am with a similar question as the last time, and for which I could not find any answer.
Note that I consider important: Normally I compile my programs in opencv with the next command:
g++ -o def program.cpp `pkg-config --cflags opencv` `pkg-config --libs opencv`
This line will create an executable whose name will be def and that I will be able to use.
I am working in a project, and as it was getting bigger, I had to define some objects, just to make everything easier and possible to handle. I create one object from the files: homogra.cpp and homogra.h the comand I used for it was:
g++ -c homogra.cpp `pkg-config --cflags opencv` `pkg-config --libs opencv`
Then, I wrote in my program.cpp the line #include "homogra.h"
And I compile like:
g++ -o def program.cpp homogra.o `pkg-config --cflags opencv` `pkg-config --libs opencv`
Until now everything is working fine.
Then I create a second object(with the same compilation line as for homogra, but this time with segmentator.cpp and segmentator.h), i wrote the line #include "segmentator.h",(in program.cpp) and I compile like:
g++ -o def program.cpp .o segmentator.o `pkg-config --cflags opencv` `pkg-config --libs opencv`
Now it is not working, and it is not recognising segmentator. I checked already if segmentator was working and everything works fine if homogra is the only include in the program.cpp.
I notice something strange. If I change the lines and I write before,in the #include lines, #include "segmentator.h" and then #include "homogra.h", then the compiler, with the same line for compiling :
g++ -o def program.cpp homogra.o segmentator.o `pkg-config --cflags opencv` `pkg-config --libs opencv`
is only recognising this time segmentator and not homogra. It is maybe a little difficult to understand, I tried to explained it as better as possible.
Any help!?
Many thanks in advance.
Here is homogra.h:
using namespace cv;
using namespace std;
#ifndef _NAMES_H
#define _NAMES_H
class homogra {
public:
Mat matCalculation( Mat img, Mat img2);
void printMatrix(Mat matrix);
};
#endif
In homogra.cpp I have all the tipical includes and homogra.h:
#include <stdio.h>
#include <stdlib.h>
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
#include <sstream>
#include "opencv2/features2d/features2d.hpp"
#include "opencv2/calib3d/calib3d.hpp"
#include "homogra.h"
And then the functions explained.
Object 2 is segmentator.h
using namespace cv;
using namespace std;
#ifndef _NAMES_H
#define _NAMES_H
class segmentator {
public:
void search(Mat img,vector<std::vector<cv::Point> >& contours);
void similar(vector<std::vector<cv::Point> >& contours,vector<std::vector<cv::Point> >& contours2,vector<int>& idx);
vector<Mat> separate(Mat img,Mat img2,vector<std::vector<cv::Point> >& contours,vector<std::vector<cv::Point> >& contours2,vector<int> idx);
};
#endif
And in segmentator.cpp I have again all the same includes, except homogra.h and instead of this one I have segmentator.h.
Program.cpp is image_reg.cpp:
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <sstream>
#include "opencv2/features2d/features2d.hpp"
#include "opencv2/calib3d/calib3d.hpp"
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include "homogra.h"
#include "segmentator.h"
using namespace cv;
using namespace std;
int main(int argc, char ** argv )
{ //Here is the code where I try to invoque two instances of homogra and segmentator.
}
If I let homogra.h as the first to be read in the includes list of image_reg.cpp then only homogra.h is recognised, if I let at the first position segmentator, then only segmentator.h instances would be created and homogra. h would not be recognised.
Thanks

Answer 1

Your include header guards are wrong. They should be unique, using the name of the source file, rather than just _NAMES_H.
So in homogra.h you should have this:
#ifndef HOMOGRA_H
#define HOMOGRA_H
...
#endif
...and in segmentator.h, you should have this
#ifndef SEGMENTATOR_H
#define SEGMENTATOR_H
...
#endif
Also, it's really bad practice to have a using namespace xxx; in a header file. You make it very difficult for your headers to coexist with others.
As Jonathan Wakely points out, beginning symbols with underscores is not a great idea, either.