堆上的QCoreApplication

Question

我需要(例如在构建库时)在堆上实例化QCoreApplication，并且我发现了以下奇怪的行为(Qt5.7)：

#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!
}

基本上，如果在分配对象后立即使用"qDebug()“，则一切都按预期进行。如果不是，则arguments()列表为空。

Answer 1

它似乎与this bug有关，它已在Qt5.9中修复，并向后移植到Qt5.6.3。解决方法很简单：

#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();
}

Answer 2

我认为修复这个错误的另一种方法是通过引用传递argc：

#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!
}

此外，你不需要在堆上创建QCoreApplication，让它作为Test的自动成员就可以了，比如QCoreApplication m_app。