QCoreApplication在堆上

Question

我有需要（例如在构建库时）在堆上实例化QCoreApplication，我发现了以下奇怪的行为（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!
}

基本上，如果在分配对象之后使用“qDebug（）”，一切都按预期工作。如果没有，arguments()列表为空。

Answer 1

它似乎与this bug有关，它在Qt 5.9中得到修复，并且向后移植到Qt 5.6.3。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

我认为另一种解决此错误的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，您无需在堆上创建QCoreApplication，将其作为Test的自动成员即可，即QCoreApplication m_app。