Qt4 QString导致错误

Question

我在编译期间没有错误，但是当我运行程序时它显示错误。请帮助我解决这个问题。

Cmake版本：3.7.2

GCC版本：6.3.0

/usr/bin/ld: CMakeFiles/Project.dir/main.cpp.o: undefined reference to symbol '_ZN7QString4freeEPNS_4DataE'
/usr/lib/x86_64-linux-gnu/libQtCore.so.4: error adding symbols: DSO missing from command line collect2: error: ld returned 1 exit status

我的代码是：

#include <iostream>
#include <QString>
#include <QtCore>
#include <QtGui>

using namespace std;

int main(int argc, char *argv[]) {
std::cout << "Hello, World!" << std::endl;

QApplication app(argc, argv);

QDialog *d = new QDialog;
d->setMinimumSize(400, 400);

QTextEdit *l = new QTextEdit(d);

const char* str = "Hello world";
QString qstr = QString::fromAscii(str);
b->setText(qstr);
d->show();

return app.exec();
}

CmakeFile： https://pastebin.com/01Qm7c4p