CODEWITHSUNDEEP
c++qt
matpen
matpen

Reputation: 291

QCoreApplication on the heap

I have the need (for example when building a library) to instantiate QCoreApplication on the heap, and I found the following strange behavior (Qt 5.7):

#include <QCoreApplication>
#include <QDebug>

class Test
{
public:
    Test(int argc, char *argv[]) {
        m_app = new QCoreApplication(argc, argv);

        //uncomment this line to make it work
        //qDebug() << "test";
    }
    ~Test() { delete m_app; }
private:
    QCoreApplication* m_app;
};

int main(int argc, char *argv[])
{
    Test test(argc, argv);
    qDebug() << QCoreApplication::arguments(); //empty list!
}

Basically, everything works as expected if "qDebug()" is used just after allocating the object. If not, the list of arguments() is empty.

Upvotes: 1

Views: 300

Answers (2)

Thomas McGuire
Thomas McGuire

Reputation: 5466

I believe another way to fix this bug is to pass argc by reference:

#include <QCoreApplication>
#include <QDebug>

class Test
{
public:
    Test(int& argc, char *argv[]) {
        m_app = new QCoreApplication(argc, argv);

        //uncomment this line to make it work
        //qDebug() << "test";
    }
    ~Test() { delete m_app; }
private:
    QCoreApplication* m_app;
};

int main(int argc, char *argv[])
{
    Test test(argc, argv);
    qDebug() << QCoreApplication::arguments(); //empty list!
}

In addition, you don't need to create QCoreApplication on the heap, having it as an automatic member of Test is fine, i.e. QCoreApplication m_app.

Upvotes: 0

matpen
matpen

Reputation: 291

It seems to be related to this bug, which was fixed in Qt 5.9 and backported to Qt 5.6.3. The workaround is simply:

#include <QCoreApplication>
#include <QDebug>

class Test
{
public:
    Test(int argc, char *argv[]) {
        //allocate argc on the heap, too
        m_argc = new int(argc);
        m_app = new QCoreApplication(*m_argc, argv);
    }
    ~Test() {
        delete m_app;
        delete m_argc;
    }
private:
    int* m_argc;
    QCoreApplication* m_app;
};

int main(int argc, char *argv[])
{
    Test test(argc, argv);
    qDebug() << QCoreApplication::arguments();
}

Upvotes: 1

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