QCoreApplication堆上

Question

我有需要（例如建立時庫）在堆上實例化QCoreApplication，我發現以下奇怪的行爲（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，一切正常如果在分配對象後立即使用「qDebug（）」，則會出現這種情況。如果不是，則arguments()的列表爲空。

Answer 1

它似乎與this bug有關，它在Qt 5.9中得到了修復，並且被回溯到了Qt 5.6.3。解決方法很簡單：

#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

我相信另一種方式來修復這個bug是按引用傳遞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，你並不需要在堆上創建QCoreApplication，其它作爲Test的自動成員是好的，即QCoreApplication m_app。