C libraries work in main.cpp but throws error in class definition

[intelharsh]

Hello people,

I am using zbar library to detect barcode. I am able to compile and run their sample code in main.cpp
Now if I make a class and include <zbar.h> in the header of that class, I get the following error :

/usr/local/include/zbar/Exception.h:144: error: the default argument for parameter 0 of 'zbar::Exception::Exception(const void*)' has not yet been parsed

Why is this happening?

[Ancient Dragon]

You need to post the code.

[intelharsh]

This is the code that works.

#include <iostream>
#include <Magick++.h>
#include <zbar.h>
#include <highgui.h>
#include <cv.h>

using namespace std;
using namespace zbar;
using namespace cv;

int main (int argc, char **argv){
if(argc < 2) return(1);

// create a reader
ImageScanner scanner;

// configure the reader
scanner.set_config(ZBAR_NONE, ZBAR_CFG_ENABLE, 1);

// obtain image data
Magick::Image magick(argv[1]);  // read an image file
int width = magick.columns();   // extract dimensions
int height = magick.rows();
Magick::Blob blob;              // extract the raw data
magick.modifyImage();
magick.write(&blob, "GRAY", 8);
const void *raw = blob.data();

// wrap image data
Image image(width, height, "Y800", raw, width * height);

// scan the image for barcodes
int n = scanner.scan(image);

cv::Mat dispImage = imread(argv[1]);

// extract results
for(Image::SymbolIterator symbol = image.symbol_begin();
    symbol != image.symbol_end();
    ++symbol) {
    // do something useful with results
    cout << "decoded " << symbol->get_type_name()
         << " symbol \"" << symbol->get_data() << '"' << endl;
      }
}
// clean up
image.set_data(NULL, 0);

return(0);
}

Now I make a dummy class.

#ifndef DUMMY_H
#define DUMMY_H

#include <zbar.h>

class dummy{
public:
    dummy();
};

#endif // DUMMY_H

This gives me an error :
/usr/local/include/zbar/Exception.h:43: error: 'NULL' was not declared in this scope
/usr/local/include/zbar/Exception.h:144: error: the default argument for parameter 0 of 'zbar::Exception::Exception(const void*)' has not yet been parsed

[Ancient Dragon]

Apparently zbar.h does not define NULL. Did you try including iostream (or some other header file that defines NULL) before zbar.h in dummy.h?

[intelharsh]

I tried including <cstddef>, <stddef.h> <stdlib.h>, <cstdlib>, <iostream>... But the problem persists!

[intelharsh]

But why is it that it works in main.cpp but not in dummy.h? If NULL is undefined, it shouldn't have worked even in main.cpp, right?

[intelharsh]

I'm sorry it workeed!!! But again, why is it that it works in main.cpp but not in dummy.h? If NULL is undefined, it shouldn't have worked even in main.cpp, right?

[cambalinho]

just for test these:

#ifndef DUMMY_H
#define DUMMY_H

#include <iostream>
#include <Magick++.h>
#include <zbar.h>
#include <highgui.h>
#include <cv.h>

using namespace std;
using namespace zbar;
using namespace cv;

class dummy{
public:
    dummy();
};

#endif // DUMMY_H

tell me if you don't get any errors

[cambalinho]

"But again, why is it that it works in main.cpp but not in dummy.h? If NULL is undefined, it shouldn't have worked even in main.cpp, right?"
i think it's the dependency libraries. like i did with code.
maybe the zbar.h depends on other header files.

[intelharsh]

@Cambalinho : the code worked... the main.cpp already had iostream included before zbar.h, which wasn't the case in dummy.h.
Thanks!