qDebug doesn't stream anything

Nasser Ahmed

Hello;
I have just start learning Qt using Qt Creator V4.13 and Qt V5.15.1, when I use qDebug(), qInfo(), qWarning() and qCritical() it doesn't show any thing in the application output.
[Edit]
I have checked 'run in terminal' and then clean and rebuild project, it now runs with "qtcreator_process_sub" with the required output of qDebug.

.pro file

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

CONFIG += c++11

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
    main.cpp \
    mainwindow.cpp

HEADERS += \
    mainwindow.h

FORMS += \
    mainwindow.ui

TRANSLATIONS += \
    ToDo_ar_EG.ts

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

MainWindow.h file

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();
private slots:
void addTask();

private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

MainWindow.cpp file

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "QtWidgets/QPushButton"
#include "QDebug"
#include <iostream>

MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
connect(ui->addTaskButton, &QPushButton::clicked, this, &MainWindow::addTask);
}

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

void MainWindow::addTask()
{
qDebug()<<"Debug button";
qInfo()<<"Information output";
qWarning()<<"Warning output";
qCritical()<<"Critical output";
}

I have spent two days searching on Google but it all the answers were about undefine QT_NO_DEBUG_OUTPUT but it's defined.
what I have tried:
include "QtDebug" instead of "qDebug"
create qtlogging.ini with content:-

[Rules]
.debug=true
qt..debug=false

Tried a clean build (clean and rebuild project) after each edit

specs:
Arch Linux (System is up to date I have just updated it)
V4.13 and Qt V5.15.1
CMake V3.18.2
Make V4.3
QMake V3.1

JonB

@Nasser-Ahmed
Everything works fine for me (without touching any qtlogging.ini, should that indeed have qt..debug=false, I don't know?), under Ubuntu with all distro-released Qts, I never compile.

One thing: add your own qInstallMessageHandler(myMessageOutput) as per https://doc.qt.io/qt-5/qtglobal.html#qInstallMessageHandler . All qDebug()/qInfo() etc. go via that. Does that even get hit for you? If it does you have some problem with the output; it it does not you have some problem with your qDebug()s etc., such as compiled to do nothing.

Another small thing: your Qt include #include statements should all be #include <something-no-slash>, so:

#include <QPushButton>
#include <QDebug>

Using your "s there could be a danger if it picking up something of your own instead of the Qt system one. Correct those as shown, just in case....