main arguments

[spetro3387]

Hi everyone, I am working on a 3D viewer using libQGLViewer. In all of the examples provided, the main function looks something like this:

int main(int argc, char** argv){
  QApplication application(argc, argv);
  Viewer viewer;
#if QT_VERSION < 0x040000
  application.setMainWidget(&viewer);
#else
  viewer.setWindowTitle("pointCloud");
#endif
  viewer.show();

  return(g_qApplication.exec()); //waits for Esc
}

The application and viewer objects need only be referenced in the main loop for all of the examples provided, but for my program, I need to call a function viewer.updateGL() that exists outside the main loop. So I made viewer global. This was not OK, QApplication complained because it needs to be constructed before the Viewer. So I made QApplication application(argc, argv); global with both arguments NULL because I don't use them. QT complained and said it needs real arguments, specifically, the first argument cannot be zero and the second must contain atleast one argument. Problem is, I have no idea how to set a string in a double pointer char (ie. char **argv). I just wasted a lot of time trying to find out and didn't come up with anything. Anyone have any ideas? I basically want this: argv[0] = "./PointCloud", where argv[0][0] to argv[0][12] would contain all the letters and a NULL terminator at the end. There has to be a simple way to do this. Thanks.

[Moschops]

Read this and do the one appropriate for Win or *nix, depending on what you're coding for.

http://doc.qt.nokia.com/latest/qcoreapplication.html#arguments

The arguments are taken from the arguments you pass to the main function when you start the programme. What command line arguments are you passing in to main?

[Fbody]

If used, the arguments to main() are always going to be at least argc = 1 and argv[0] = "[I]executableName[/I]" . As you add more command line arguments, argc will increase and argv will get more elements.

I find that it tends to help if you draw parallels between main() and user-defined functions. Try to think of argv as an array of values and argc as an "arraySize" variable. To be able to use an array (argv) effectively as an argument/parameter, you need to know the size (argc).

Thus, in this case, if you want to be able to use "./PointCloud" as your program name, that is the value that will be stored in argv[0] automatically. Any command-line switches/arguments will be stored in argv[1] or later.

[chrjs]

I don't know much about libQGLViewer, but you could try keeping viewer local and just making a variable that points to viewer global, and call updateGL using that pointer.

[spetro3387]

I know how the command line arguments work. That is not my question. I have to make the line

QApplication application(argc, argv);

global. In order to do so I have to make two arguments. As stated in my original post, I do not know how I can set a string to a double char pointer.

chrjs,
So I already tried that. That was actually one of the first things I thought of. So as I was typing this response to you, on a hunch, I decided to try it again. I made a global Viewer *view, then set that equal to &viewer in main(), then in my function call I used (*view).updateGL(); and I was getting an error when I executed the function. Well the function was this:

void on_trackbar(int h){
    (*view).updateGL();
}

on_trackbar(int h) is an openCV function that is called whenever the trackbar is moved. Turns out when I initialize the trackbar (which was in main(), before the view = &viewer) OpenCV calls this on_trackbar() function. So that's where the problem was. The (*view).updateGL() function was being called in on_trackbar() without me knowing. So I put view = &viewer; before the trackbar initialization and everything worked. Thanks, without your post I would have never tried that again.