error: undefined symbol:QZXing::QZXing(QObject*)

这个错误表示在编译或链接时找不到QZXing类的构造函数QZXing(QObject*)的定义。要解决这个错误，你需要确保已正确包含QZXing库，并且在代码中正确实例化QZXing类并传入QObject指针。你需要检查你的代码是否正确使用了QZXing库，并且检查是否正确链接该库。如果你使用的是C++语言，还需要确保在代码中包含了QZXing类的头文件。

相关问题

error: undefined reference to `receiveMessgaeThread::receiveMessgaeThread(QObject*)'

这个错误提示说的是无法找到 `receiveMessgaeThread` 类的构造函数的定义，可能是因为你在代码中声明了这个类的构造函数，但是没有在实现文件中实现它。

你需要确保在实现文件中定义了这个类的构造函数，比如：

receiveMessgaeThread::receiveMessgaeThread(QObject *parent) : QThread(parent)
{
    // 构造函数的实现
}

如果你已经实现了这个构造函数，但是还是出现了这个错误，那么可能是因为你没有将实现文件加入到编译中。你需要在你的项目文件（.pro）中添加这个实现文件，比如：

SOURCES += receiveMessgaeThread.cpp

这样就可以解决这个错误了。

error: undefined reference to `QUdpSocket::QUdpSocket(QObject*)'

This error message indicates that the linker is unable to find a reference to the constructor of the QUdpSocket class that takes a QObject pointer as its argument. This could be due to a missing include statement or a missing library in your project.

To resolve this issue, make sure that you have included the necessary header file for the QUdpSocket class and that you have added the appropriate library in your project settings. Additionally, you may also want to check if there are any conflicting definitions or declarations of the QUdpSocket class in your code.