cout does no print in QtCreator

Question

I saw this question already on this forum but I do not know why the proposed answer does not work in my case. So I try to ask for other slution.

I just got my Qt creator running under Linux.

I do not understand why my:

cout << "This does not appear";

Does not print in console while qdebug does

qDebug() << "This appears";

This is what is contained in my .pro file:

QT       += core gui

TARGET = aaa
TEMPLATE = app


SOURCES += main.cpp\
        mainwindow.cpp \
    IeplcModule.cpp

HEADERS  += mainwindow.h \
    IeplcModule.h

FORMS    += mainwindow.ui

#enable console
CONFIG += console

Any idea?

Does the output appear when the program stops? If yes, it's probably just a missing flush (add a std::endl) — Steffen, Sep 27 '11 at 08:13
Debug output is shown directly. The `` equivalent of `qDebug()` is `cerr <<`, that doesn't need flushing either. — MSalters, Sep 27 '11 at 09:01

score 29 · Accepted Answer · edited May 28 '21 at 21:48

29

Try with:

cout << "asdf" << endl;

Possibly Qt sets up iostream in order to flush only at new line.

edited May 28 '21 at 21:48

eyllanesc

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answered Sep 27 '11 at 08:39

robermorales

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5

+1 For the correct answer and explanation, by the way you didn't suggest using qDebug() as everyone did. – RajaRaviVarma Oct 17 '12 at 09:39
Actually, `endl` is a newline *plus* flush command. Similar to `"\n" << flush` – steffen Mar 18 '16 at 09:23

score 3 · Answer 2 · answered Mar 01 '19 at 00:21

When debugging with CDB (Windows debugger) and running application not in the dedicated terminal window, but within QtCreator output panel, there is an issue with std::cout/std::cerr. qDebug works because it has a trick for this case. So, the only solution in this case is enable the "run in terminal" option. For more infor please follow the link above to the Qt bug tracker.

score 1 · Answer 3 · edited Sep 11 '12 at 23:32

1

Did you #include <iostream>? I did not see any includes in the code. I assume that qdebug and cout are very similar.

edited Sep 11 '12 at 23:32

jonsca

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answered Sep 11 '12 at 19:25

Steve Volkmen

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This question has already been solved by the accepted answer. – Austin Henley Sep 25 '12 at 02:40

score 1 · Answer 4 · answered Sep 27 '11 at 08:20

1

Is it possible that STDOUT is redirecting? qDebug prints to STDERR by default.

answered Sep 27 '11 at 08:20

spraff

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score 0 · Answer 5 · answered Feb 21 '20 at 08:11

0

Make sure you have console config enabled in your .pro file. I.e. :

CONFIG += console

answered Feb 21 '20 at 08:11

Alexander Dyagilev

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score 0 · Answer 6 · answered Jan 30 '23 at 17:16

You can run this program from CMD and it will print some messages to the console:

/* Create a .pro file with this content:
QT += core gui widgets
SOURCES += main.cpp
TARGET = app
-------------------------------
Build and run commands for CMD:
> qmake -makefile
> mingw32-make
> "release/app"
*/

#ifdef _WIN32
#include <windows.h>
#endif

#include <QtCore/QFile>
#include <QtCore/QString>
#include <QtCore/QIODevice>
#include <QtWidgets/QApplication>
#include <QtWidgets/QWidget>

#include <iostream>

class Widget : public QWidget
{
public:
    Widget()
    {
        setWindowTitle("My Title");
        QString path("assets/text.txt");
        std::cout << std::endl;
        std::cout << "hello1" << std::endl;
        std::cout << path.toStdString() << std::endl;
        std::cout << "hello2" << std::endl;
    }
};

int main(int argc, char *argv[])
{
#ifdef _WIN32
    if (AttachConsole(ATTACH_PARENT_PROCESS))
    {
        freopen("CONOUT$", "w", stdout);
        freopen("CONOUT$", "w", stderr);
    }
#endif

    QApplication app(argc, argv);
    Widget w;
    w.show();
    return app.exec();
}

cout does no print in QtCreator

6 Answers6