QT中的Q_OBJECT(对vtable xxx的未定义引用) [英] Q_OBJECT in QT (undefined reference to vtable xxx)

问题描述

我写了一个简单的测试，如下所示:

I wrote a simple test as follow:

#include <QCoreApplication>
#include <QObject>

class Foo : public QObject
{
   Q_OBJECT
};

class foo1
{
};

int main(int argc, char* argv[])
{
QCoreApplication a(argc, argv);
Foo f;
return a.exec();
}

哪个给我一个错误:

错误:对"vtable for Foo"的未定义引用:

error: undefined reference to `vtable for Foo':

但是，当我将 Foo f 更改为 Foo f()时，它可以正常执行.
所以我的问题是 f 和 f()有什么区别?

However, when I change Foo f to Foo f(), it complies without any error.
So my question is what is the different between f and f()?

推荐答案

添加括号使其成为函数声明.实际上没有创建任何对象，因此不会发生错误.

Adding the parenthesis makes it a function declaration. No object is actually created, so the error doesn't happen.

Foo f; //declaration of variable of type Foo

Foo f(); //declaration of function taking no args and returning Foo

针对Foo的vtable的未定义引用是因为您添加了对 Q_OBJECT 的调用，而没有再次运行qmake.一旦运行，该错误应消失.

The undefined reference to vtable for Foo error is because you added a call to Q_OBJECT without running qmake again. Once it's run, the error should disappear.

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