How to pass argc and argv to MainWindow object

CroCo

I'm working in a project related to ROS. I've modified CMake and it is working fine. ROS requires to call this function ros::init(argc,argv, std::string) to initialize the library. Qt also needs this QApplication. To solve this issue, I've modified the MainWindow(QWidget *parent=nullptr) to MainWindow(QWidget *parent=nullptr, int argc=0,char** argv="") but it yields the following error

error: cannot intialize a parameter of type 'char** with an lvalue of type 'const char[3]'
note: passing argument to parameter 'argv' here

In the main function. I need this

QApplication a(argc,argv);
MainWindow w(argc,argv);

Any suggestions!

JonB

@CroCo
As said, I don't know why you are wanting to call ros::init() from MainWindow anyway. When it's simple and easy to call it from main().

In fact if you read http://wiki.ros.org/roscpp/Overview/Initialization and Shutdown you see stuff like

As mentioned above, calling ros::init() with argc and argv will remove ROS arguments from the command line

It certainly seems to belong next to QApplication(argc, argv). And it might even be better to put it before that line in some ways.

Christian Ehrlicher

@CroCo said in How to pass argc and argv to MainWindow object:

MainWindow(QWidget parent=nullptr, int argc=0,char* argv="")

MainWindow w(argc,argv);

And where is your QWidget *parent parameter?

Also you should take a look at QCoreApplication::arguments() instead passing plain argc/argv

CroCo

@Christian-Ehrlicher QApplication::arguments().at(0).toInt() solves the first argument but I got stuck with argv. How to capture the argument as char**?

Christian Ehrlicher

Again: the signature is QWidget *, int,char**, you pass int, char** - how should this work? You have to pass a proper QWidget pointer (or a nullptr) or change the signature - basic C stuff.

JonB

@CroCo said in How to pass argc and argv to MainWindow object:

ros::init(argc,argv, std::string)

Can you not do this in the main(int argc, char **argv) function, which is where those variables are available? Next to where you have QApplication(argc, argv). MainWindow isn't even the same thing as main(), it doesn't have anything to do with initialisation so why is your ros::init() (which looks like a one-time program start-up thing to me) inside it?

As far as I know, you cannot guarantee to access what is passed as argc, argv to a C++ main() anywhere else, without passing those variables on. C++ does not make them available, it may have done its own processing on whatever the OS passed from its "command line" or other invocation method before passing as main() parameters.

CroCo

@Christian-Ehrlicher I wasn't aware of QApplication::arguments(). Now I've changed the MainWindow to its original form. Now I need to access arguments inside MainWindow constructor so I can initiate ROS. No problem with the first argument but the second one I don't know which function that convert QString to char**. I've tried .c_str() with no luck.

JonB

@CroCo
As said, I don't know why you are wanting to call ros::init() from MainWindow anyway. When it's simple and easy to call it from main().

In fact if you read http://wiki.ros.org/roscpp/Overview/Initialization and Shutdown you see stuff like

As mentioned above, calling ros::init() with argc and argv will remove ROS arguments from the command line

It certainly seems to belong next to QApplication(argc, argv). And it might even be better to put it before that line in some ways.

Christian Ehrlicher

How about looking at the QString documentation? QString::toLatin1(), QString::toUtf8() for example.
And why do you need a char** at all? What are you trying to do?