Declaration of function and use it

jsulm

@gauravsharma0190 Can you please post the code which causes the compiler error? The code you posted is not of interest. Where is mainwindow::ontrackball? Please post mainwindow.h and mainwindow.cpp.

jsulm

@gauravsharma0190 Did you put void on_track_ball(int void*) inside mainwindow class in mainwindow.h? The error message sounds like you put it outside of mainwindow. It should be like:

// mainwindow.h
class mainwindow
{
private:
    void on_track_ball(int, void*);
}

// mainwindow.cpp
void mainwindow::on_track_ball(int, void*)
{
}

jsulm

@gauravsharma0190 The code you posted does not use Qt as far as I can see. You will need to change more if you want to use Qt.

gauravsharma0190

@jsulm
Yes i did the same but error occurs.
i couldnt find where is problem

jsulm

@gauravsharma0190 That's why I'm asking for the code! Without it I cannot find the problem as well.

gauravsharma0190

So please tell me what i send you sir.
i give you my all the code .
Now please tell me only that how to invoke code when i click the button

jsulm

@gauravsharma0190 I already said that: mainwindow.h and mainwindow.cpp
I provided you a link where you can learn how signals and slots in Qt work, here it is again: http://doc.qt.io/qt-5.7/signalsandslots.html
Please read it! Else you will not be able to use Qt much - signals/slots is one of the most important concepts in Qt.
Short description: QPushButton has a signal clicked() (see http://doc.qt.io/qt-5/qabstractbutton.html#clicked). This signal is emitted when user presses the button. You need to connect a slot to that signal, then this slot will be called when you press the button.

jsulm

@gauravsharma0190 A small example application with a button:

// main.cpp
#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

// mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private slots:
    void doSomethingWhenButtonPressed(bool);

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

// mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QDebug>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    connect(ui->pushButton, SIGNAL(clicked(bool)), this, SLOT(doSomethingWhenButtonPressed(bool)));
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::doSomethingWhenButtonPressed(bool)
{
    qDebug() << "Button pressed!";
}

gauravsharma0190

@jsulm
i got it tht how to use push button.
using connect i know it because i did it with my code.
but i want to know how to declare and defination of function in qt and use these in pushbutton.
Like we do in c as declare and defination of function and use it main()
as in c++ declare and defination and use it in main function or classes.
please give me a simple example or link.

like

jsulm

@gauravsharma0190 I don't understand the problem. Qt is not a programming language. You use C++ with qt. So you define and use your function/method as any other function/method in C++.
I already gave you an example showing how to use a push button to execute a method when the button is clicked. Isn't that what you want to do?
Please explain what is the problem! Maybe some code?

mrjj

@gauravsharma0190

Hi
As @jsulm says, its a bit unclear what you ask.
You can use functions just like you would in c, but in c++ gui program,
normally main is the not the center of the application. QMainwindow is or some other class.
Maybe this helps:

//--------------------
//std c program
//--------------------
void myfunc() {};

void main() {
  myfunc();
}

//--------------------
//c++ function being a class member ( lives in class)
//--------------------
class Mainwindow {
 public:
  void myfunc();
};
(in cpp)
Mainwindow::myfunc() {
  //code
}
//--------------------
//c++ with "outside" function ( non member function)
//--------------------
(in .h)
void outsidefunc(); // define

class Mainwindow {
 public:
  void myfunc();
};
(in cpp)

void outsidefunc() { // implement
}

Mainwindow::myfunc() {
  outsidefunc();
}

gauravsharma0190

Yes sir see i have a c code of opencv which process the image.
Now my problem is i want to use this code with qt as when button is pressed my push button calls the function of that C code in which main part of Process is defined.
Here is the C code.
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"
#include <stdlib.h>
#include <stdio.h>

using namespace cv;

/// Global variables

Mat src, src_gray;
Mat dst, detected_edges;

int edgeThresh = 1;
int lowThreshold;
int const max_lowThreshold = 100;
int ratio = 3;
int kernel_size = 3;
char* window_name = "Edge Map";

/**

@function CannyThreshold
@brief Trackbar callback - Canny thresholds input with a ratio 1:3
/
void CannyThreshold(int, void)
{
/// Reduce noise with a kernel 3x3
blur( src_gray, detected_edges, Size(3,3) );

/// Canny detector
Canny( detected_edges, detected_edges, lowThreshold, lowThreshold*ratio, kernel_size );

/// Using Canny's output as a mask, we display our result
dst = Scalar::all(0);

src.copyTo( dst, detected_edges);
imshow( window_name, dst );
}

/** @function main /
int main( int argc, char* argv )
{
/// Load an image
src = imread( argv[1] );

if( !src.data )
{ return -1; }

/// Create a matrix of the same type and size as src (for dst)
dst.create( src.size(), src.type() );

/// Convert the image to grayscale
cvtColor( src, src_gray, CV_BGR2GRAY );

/// Create a window
namedWindow( window_name, CV_WINDOW_AUTOSIZE );

/// Create a Trackbar for user to enter threshold
createTrackbar( "Min Threshold:", window_name, &lowThreshold, max_lowThreshold, CannyThreshold );

/// Show the image
CannyThreshold(0, 0);

/// Wait until user exit program by pressing a key
waitKey(0);

return 0;
}
Now i make a Push button Name Process_image in MainWindow.ui and connect to slot as clicked() by right clicking of mouse.
here comes the slot to mainwindow.cpp
void mainwidow::Process_image_clicke()
{
}
Now i don't understand how to make function of my C code and use it in Pusebutton.

mrjj

well you should make a pair of .h and .cpp files for the opencv stuff
lets call it myopenvc.h and myopenvc.cpp

in h. you can declare the function u want rest of program to use

void setupOPENVC();

and in .cpp

void setupOPENVC() {
// the code from the old c- main. !
src = imread( argv[1] );
xxxx
}

then in Mainwindow.cpp
#include "myopencv.h"

and now u can call your function
void mainwidow::Process_image_clicke()
{
setupOPENVC();
}

ps:
In event driven programs. ( like Qt)
stuff like
waitKey(0);
or FOREVER loops are not to be used as it
will freeze the program and it stops working.

gauravsharma0190

@mrjj Hello i did it sir.
but error occurs.

gauravsharma0190

@jsulm Yes sir see i have a c code of opencv which process the image.
Now my problem is i want to use this code with qt as when button is pressed my push button calls the function of that C code in which main part of Process is defined.
Here is the C code.
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"
#include <stdlib.h>
#include <stdio.h>

using namespace cv;

/// Global variables

Mat src, src_gray;
Mat dst, detected_edges;

int edgeThresh = 1;
int lowThreshold;
int const max_lowThreshold = 100;
int ratio = 3;
int kernel_size = 3;
char* window_name = "Edge Map";

/**

@function CannyThreshold
@brief Trackbar callback - Canny thresholds input with a ratio 1:3
/
void CannyThreshold(int, void)
{
/// Reduce noise with a kernel 3x3
blur( src_gray, detected_edges, Size(3,3) );
/// Canny detector
Canny( detected_edges, detected_edges, lowThreshold, lowThreshold*ratio, kernel_size );

/// Using Canny's output as a mask, we display our result
dst = Scalar::all(0);

src.copyTo( dst, detected_edges);
imshow( window_name, dst );
}

/** @function main /
int main( int argc, char* argv )
{
/// Load an image
src = imread( argv[1] );

if( !src.data )
{ return -1; }

/// Create a matrix of the same type and size as src (for dst)
dst.create( src.size(), src.type() );

/// Convert the image to grayscale
cvtColor( src, src_gray, CV_BGR2GRAY );

/// Create a window
namedWindow( window_name, CV_WINDOW_AUTOSIZE );

/// Create a Trackbar for user to enter threshold
createTrackbar( "Min Threshold:", window_name, &lowThreshold, max_lowThreshold, CannyThreshold );

/// Show the image
CannyThreshold(0, 0);

/// Wait until user exit program by pressing a key
waitKey(0);

return 0;
}
Now i make a Push button Name Process_image in MainWindow.ui and connect to slot as clicked() by right clicking of mouse.
here comes the slot to mainwindow.cpp
void mainwidow::Process_image_clicke()
{
}
Now i don't understand how to make function of my C code and use it in Pusebutton.

jsulm

@gauravsharma0190 Well, you can put that C code in

void mainwidow::Process_image_clicke()
{
    // Put C code here
}

But I'm not sure whether you should remove waitKey(0); as it could be problematic in a Qt program.

gauravsharma0190

@jsulm
i put it into Process_image_click()
{
//code
}
but error occurs.
as ontrackball function not declare

jsulm

@gauravsharma0190 What is ontrackball? Where is it declared? Do you have to include a header file where it is declared?

gauravsharma0190

Yes it is function which is declare in the Opencv C code.
Here is the function.
@brief Trackbar callback - Canny thresholds input with a ratio 1:3
/
void onTrackball(int, void)
{
/// Reduce noise with a kernel 3x3
blur( src_gray, detected_edges, Size(3,3) );
/// Canny detector
Canny( detected_edges, detected_edges, lowThreshold, lowThreshold*ratio, kernel_size );

/// Using Canny's output as a mask, we display our result
dst = Scalar::all(0);

src.copyTo( dst, detected_edges);
imshow( window_name, dst );
}

gauravsharma0190

@jsulm Yes it is function which is declare in the Opencv C code.
Here is the function.
@brief Trackbar callback - Canny thresholds input with a ratio 1:3
/
void onTrackball(int, void)
{
/// Reduce noise with a kernel 3x3
blur( src_gray, detected_edges, Size(3,3) );
/// Canny detector
Canny( detected_edges, detected_edges, lowThreshold, lowThreshold*ratio, kernel_size );

/// Using Canny's output as a mask, we display our result
dst = Scalar::all(0);

src.copyTo( dst, detected_edges);
imshow( window_name, dst );
}

less than a minute ago