Functions and Object Files C++ will NOT Compile

[KonaRurrik]

I have a project I'm coding in C++ with the OpenCV library. I want to separate the project into (right now at least) 6 files. I have xPush.cpp xPush.h ColorPick.cpp ColorPick.h ColorExtract.cpp ColorExtract.h

ColorPick.h has the following code:

#ifndef STDX
#define STDX
#include <stdio.h>
#include <stdlib.h>
#include <cv.h>
#include <cvaux.h>
#include <highgui.h>
#include <math.h>
#include <stdlib.h>
#endif

// Check to see if this header was called already
#ifndef COLORPICK_H
// Define
#define COLORPICK_H

// Declarations for ColorPick
IplImage *cp_LIVE;
IplImage *cp_EX;
int color;
int end;
int key;

// Class passes color thresholds back and forth (BGR format)

class cThresh {
	public:
	int mC;
	int Cp1;
	int Cp2;
	};
	
#endif 

It is called in xPush.h which has the following code:

#ifndef STDX
#define STDX
#include <stdio.h>
#include <stdlib.h>
#include <cv.h>
#include <cvaux.h>
#include <highgui.h>
#include <math.h>
#include <stdlib.h>
#endif


// Check to see if this has already been included
#ifndef XPUSH_H
// Define
#define XPUSH_H

#include "ColorPick.h"
#include "ColorExtract.h"

// Declare IplImage variables for xPush
IplImage *img_LIVE=NULL;		// Live camera capture image
IplImage *img_CURR=NULL;		// Current camera frame
IplImage *img_COLX=NULL;		// Extracted Color Image

// Declare Color Thresh objects
cThresh Color1;
cThresh Color2;



#endif 

This is in turn called by xPush.cpp:

//////////////////////////////////////////
//	Main C++ file for xPush		//
//////////////////////////////////////////

#include "xPush.h"

// Prototype Additional C++ files
int ColorExtract(IplImage *img_SOURCE, IplImage *img_DEST);
int ColorPick(cThresh Color1, cThresh Color2);




int tester;

// Main function call

int main( int argc, char **argv){

// First call ColorPick so we can chose the colors to be used
tester = ColorPick(Color1, Color2);













/////////////////////////////////
// Below curly ends main function
}

The last important file is ColorPick.cpp (function doesn't really use inputs right now)

#include "ColorPick.h"

int ColorPick(cThresh C1, cThresh C2){

// Begin by calling up a live feed
CvCapture *cpLiveFeed=NULL;		// Capture placeholder (improves speed)
cpLiveFeed=cvCaptureFromCAM(0);		// Set up the area for captured frames

// Loop for feed
while (end != 1){

// Capture frames
cvGrabFrame (cpLiveFeed);
cp_LIVE = cvRetrieveFrame (cpLiveFeed);

// Image Creation
cp_EX=cvCreateImage(cvGetSize(cp_LIVE),8,1);





// Display windows
cvNamedWindow("Live",CV_WINDOW_AUTOSIZE);
	cvShowImage("Live",cp_LIVE);
cvNamedWindow("Color Extraction",CV_WINDOW_AUTOSIZE);
	cvShowImage("Color Extraction",cp_EX);
	
	
// Create Trackbars on Live	
cvCreateTrackbar("Main Color Channel","Live",&color,2,NULL);	

// Wait for Kepress to finish the color threshold selection
key=cvWaitKey(20);
if (key != -1)
end = 1;


// Below ends live feed while loop
}




return 1;
/////////////////////////////
// Below curly ends ColorPick
}

The makefile is:

xPush: xPush.cpp xPush.h ColorExtract.o ColorPick.o
	g++ xPush.cpp ColorExtract.o ColorPick.o `pkg-config --libs --cflags opencv` -o xPush

ColorExtract.o: ColorExtract.cpp ColorExtract.h
	g++ -c ColorExtract.cpp `pkg-config --libs --cflags opencv` -o ColorExtract.o
	
ColorPick.o: ColorPick.cpp ColorPick.h
	g++ -c ColorPick.cpp `pkg-config --libs --cflags opencv` -o ColorPick.o

And the g++ output is:

 make
g++ -c ColorExtract.cpp `pkg-config --libs --cflags opencv` -o ColorExtract.o
g++ -c ColorPick.cpp `pkg-config --libs --cflags opencv` -o ColorPick.o
g++ xPush.cpp ColorExtract.o ColorPick.o `pkg-config --libs --cflags opencv` -o xPush
ColorPick.o:(.bss+0x0): multiple definition of `cp_LIVE'
/tmp/ccqugB5e.o:(.bss+0x0): first defined here
ColorPick.o:(.bss+0x4): multiple definition of `cp_EX'
/tmp/ccqugB5e.o:(.bss+0x4): first defined here
ColorPick.o:(.bss+0x8): multiple definition of `color'
/tmp/ccqugB5e.o:(.bss+0x8): first defined here
ColorPick.o:(.bss+0xc): multiple definition of `end'
/tmp/ccqugB5e.o:(.bss+0xc): first defined here
ColorPick.o:(.bss+0x10): multiple definition of `key'
/tmp/ccqugB5e.o:(.bss+0x10): first defined here
/tmp/ccqugB5e.o: In function `main':
xPush.cpp:(.text+0x3f): undefined reference to `ColorPick(cThresh, cThresh)'
collect2: ld returned 1 exit status
make: *** [xPush] Error 1

As far as I can tell, I'm doing everything correctly, but apparently g++ doesnt like one of my #ifndef statements or definitions or something.

Any suggestions?

[firedraco]

You are defining global variables multiple times (by including the .h files in different .cpp files), which is why you are getting the error.

For example:

//some_include.h
#ifndef myinc
#define myinc
int some_global;
#endif 

//1.cpp
#include "some_include.h" 

//2.cpp
#include "some_include.h" //Error, some_global is defined twice when you link them together 

[Albatross]

It's probably a good idea to use the extern keyword, and define your variables in ONE cpp file.

-Albatross

[KonaRurrik]

Thank you both. My solution was to take the function specific declarations and put them into the .cpp file instead of the .h file.

Can I keep class definitions in an .h file? For instance can i leave the cThresh class inside ColorPick.h? It lets me compile and run, so I'm guessing its fine, Im just asking if thats the best practice, or if I should create a separate class.h to contain all of my classes? Is there a best practice?

Thanks so much for your quick replies!