With this code
#include "mainwindow.h"
#include <QApplication>
#include <iostream>
#include <QDir>
#include <QTextStream>
int main(int argc, char *argv[]){
QApplication a(argc, argv);
QTextStream out(stdout);
out << QDir::currentPath();
std::cout << "Why is that?";
MainWindow mainWindow;
mainWindow.show();
return a.exec();
}
Both messages printed only after closing Main Window of my app, why is this?
I tried to debug, debugger thinks that he done with this line, but I see no messages.
extern std::ostream cout; is buffered, so it may choose when to flush its buffer to stdout. In your case, it is doing it when your program is terminating.
You can tell std::ostream to flush using std::flush, as such:
std::cout << "Why is that?" << std::flush;
Related
I'm trying to get global position of the mouse however the functions mentioned in older topics are either deprecated or not working as intended. I have tried QCursor::pos() as seen below but it didn't work as intended.
#include <QtCore/QCoreApplication>
#include <QCursor>
#include <iostream>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
while(1)
{
std::cout << QCursor::pos().x() << " " << QCursor::pos().y() << std::endl;
}
return a.exec();
}
Output: 2147483647 2147483647
It is very simple. QCursor is in the Gui module of Qt see here, so you have to change QCoreApplication to QGuiApplication and then it works (already tested it).
I am learning C++ with Qt. I have installed Qt 5.15 and am using VS2019. I have the below code (as per an example in a textbook I am working through):
#include <QtGui>
int main(int argc, char* argv[])
{
QApplication app(argc, argv);
QTextStream cout(stdout);
//declarations of variables
int answer = 0;
do{
//local variables
int factArg = 0;
int fact(1);
factArg = QInputDialog::getInt(0, "Factorial Calculator", "Factorial of:", 1);
cout << "User entered: " << factArg << endl;
int i = 2;
while (i <= factArg) {
fact = fact * i;
++i;
}
QString response = QString("The factorial of %1 is %2.\n%3").arg(factArg).arg(fact).arg("Do you want to compute another factorial?");
answer = QMessageBox::question(0, "Play again?", response, QMessageBox::Yes | QMessageBox::No);
} while (answer == QMessageBox::Yes);
return EXIT_SUCCESS;
}
However, I am recieving the below error when creating an instance of QApplication as app:
Incomplete Type is not Allowed
I am also recieving the below error for the QInputDialog and QMessageBox classes:
name followed by '::' must be a class or namespace name
I am not sure why this is happening - presumably something with a namespace, but I am not sure what scope to provide. I have searched the web but to no avail.
UPDATE
Adding the below header references give cannot open source file error for each.
#include <QApplication>
#include <QInputDialog>
#include <QMessageBox>
I have also added suggestions from the comments to my code, now below:
#include <QtGui>
#include <iostream>
using namespace std;
int main(int argc, char* argv[])
{
QApplication app(argc, argv);
QTextStream cout(stdout);
//declarations of variables
int answer = 0;
do{
//local variables
int factArg = 0;
int fact(1);
factArg = QInputDialog::getInt(0, "Factorial Calculator", "Factorial of:", 1);
cout << "User entered: " << factArg << endl;
int i = 2;
while (i <= factArg) {
fact = fact * i;
++i;
}
QString response = QString("The factorial of %1 is %2.\n%3").arg(factArg).arg(fact).arg("Do you want to compute another factorial?");
answer = QMessageBox::question(0, "Play again?", response, QMessageBox::Yes | QMessageBox::No);
} while (answer == QMessageBox::Yes);
return EXIT_SUCCESS;
}
But I am still recieving the same errors.
You have to include some qt headers in the app... that is the meaning of the message
you just need to add this to your code
#include <QApplication>
#include <QInputDialog>
#include <QMessageBox>
The correct headers to include are the following:
#include <QtWidgets/QApplication>
#include <QtWidgets/QInputDialog>
#include <QtWidgets/QMessageBox>
Once declaring these, the compiler accepts the code.
I'm going to cut and paste a working program for you.
Qt seems to have a bunch of forward definitions. I can tell I'm missing the right include file if I try to get the IDE to actually help me select a method call. In short, you pretty much have to #include every widget type or other class you're going to use. I haven't run into any shortcuts.
#include <QApplication>
#include "MainWindow.h"
using namespace std;
/**
* Main entry point.
*/
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
MainWindow mainWindow;
mainWindow.show();
return app.exec();
}
I wrote a C++ program in Qt that used dynamic memory allocation, and I made sure to include the free() call at the end. However, when the program reaches the free statement, it crashes. (I know this because the test that I added never printed after the free statements) Anyway, here's the code:
#include <QCoreApplication>
#include <QSerialPort>
#include <iostream>
#include <time.h>
#include <stdlib.h>
#include <Windows.h>
using namespace std;
int main(int argc, char *argv[])
{
QSerialPort serial0;
//serial.open(serial);
serial0.setBaudRate(QSerialPort::Baud9600);
serial0.setDataBits(QSerialPort::Data8);
serial0.setParity(QSerialPort::NoParity);
serial0.setStopBits(QSerialPort::OneStop);
serial0.setFlowControl(QSerialPort::NoFlowControl);
char *com="com";
int number;
char *comPlusNumber;
comPlusNumber=(char*) malloc(8*sizeof(char));
int j=10000;
while(j>0)
{
number=j;
sprintf(comPlusNumber, "%s%d",com,number);
//printf("%s \n",comPlusNumber);
serial0.setPortName(comPlusNumber);
serial0.open(QIODevice::ReadWrite);
if(serial0.isOpen()==true)
{
printf("YES*****************");
printf("%s \n",comPlusNumber);
}
else
//printf("No %d\n", number);
serial0.close();
j--;
}
free(com);
free(comPlusNumber);
printf("\n\n Test");
//QCoreApplication a(argc, argv);
//return a.exec();
}
I just wanted to make sure that I wasn't creating a memory leak.
Use the framework. You've got the power of Qt!
There are several problems:
The C-style string manipulations are unnecessary and wrong. Use QString:
auto name = QStringLiteral("COM%1").arg(i);
You can't use the serial port without a QCoreApplication instance present.
You shouldn't be testing for the presence of a port by iterating what you think might be valid ports. This is non-portable and unnecessary. Get a list of ports to start with.
Thus:
// https://github.com/KubaO/stackoverflown/tree/master/questions/simple-serial-35181906
#include <QtCore>
#include <QtSerialPort>
int main(int argc, char ** argv) {
QCoreApplication app{argc, argv};
QSerialPort serial;
serial.setBaudRate(QSerialPort::Baud9600);
serial.setDataBits(QSerialPort::Data8);
serial.setParity(QSerialPort::NoParity);
serial.setStopBits(QSerialPort::OneStop);
serial.setFlowControl(QSerialPort::NoFlowControl);
for (auto port : QSerialPortInfo::availablePorts()) {
serial.setPort(port);
serial.open(QIODevice::ReadWrite);
if (serial.isOpen()) {
qDebug() << "port" << port.portName() << "is open";
serial.close();
} else
qDebug() << "port" << port.portName() << "couldn't be opened";
}
}
Here's the output on my machine:
port "cu.serial1" is open
port "cu.usbserial-FTELA9I5" is open
port "cu.usbserial-PX9A3C3B" is open
You can only free what you dynamically allocated. You never dynamically allocated anything for com, so passing it to free is an error. It's equivalent to free("com"); which attempts to free a string constant.
why when i want to check .exe file this program will print false but when i add .txt file and check prints True?
i mean its only recognize .txt file not .exe
#include <QCoreApplication>
#include <QFile>
#include <QDebug>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QFile read("C:\\Users\\Ramin\\AppData\\Roaming\\Microsoft\\Windows\\Start Menu\\Programs\\Startup\\Time.exe");
if(read.exists()){
qDebug()<<"True";
}
else{
qDebug()<<"False";
}
return a.exec();
}
thanks in advance
I wrote a program to output a random quote from a QStringList to a console window, program runs but I can't figure out why nothing appears in the window. Please help
here is the code:
#ifndef RANDOMADVICE_H
#define RANDOMADVICE_H
#include <QString>
#include <QStringList>
class randomAdvice
{
public:
randomAdvice();
QString returnAdvice();
private:
QStringList randomList;
QString output;
};
#endif // RANDOMADVICE_H
here is the cpp file randomadvice.cpp
#include "randomadvice.h"
#include "cstdlib"
#include "ctime"
#include <QString>
randomAdvice::randomAdvice()
{
randomList = QStringList()
<< "In order to succeed, your desire for success should be greater than your fear of failure. - Bill Cosby"
<< "Always be yourself, express yourself, have faith in yourself, do not go out and look for a successful personality and duplicate it. - Bruce Lee"
<< "A successful man is one who can lay a firm foundation with the bricks others have thrown at him. - David Brinkley"
<< "Strive not to be a success, but rather to be of value. - Albert Einstein"
<< "To succeed in life you need 2 things: Ignorance and confidence. - Mark Twain"
<< "Success is a lousy teacher. It seduces smart people into thinking they can't lose. - Bill Gates"
<< "Remembering that you are going to die is the best way I know to avoid the trap of thinking that you have something to lose. You are already naked. There is no reason not to follow your heart. - Steve Jobs";
}
QString randomAdvice::returnAdvice()
{
srand(time(NULL));
output = randomList.at(rand() % randomList.size());
return output;
}
and the main file:
#include "randomadvice.h"
#include <QtCore/QCoreApplication>
#include <QTextStream>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QTextStream out(stdout);
randomAdvice ra;
QString adviceString = ra.returnAdvice();
out << adviceString;
return a.exec();
}
QTextStream buffer the output until it is flushed or a newline is written.
You can either add out.flush() after out << adviceString or change out << adviceString to out << adviceString << endl.
Try QTextStream out(stdout, QIODevice::WriteOnly);