Wrong compiling result by QT!!??

[greenoaktree]

These are two of my helloworld :
without QT class

#include <iostream>
int main()
{
    std::cout<<"haha"<<std::endl;
 
    return 0;
}

#include <iostream>
int main()
{
    std::cout<<"haha"<<std::endl;

    return 0;
}

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with QT class

#include <QtDebug>
int main( )
{
qDebug() << "Hello Qt World!";
return 0;
}

#include <QtDebug>
int main( )
{
qDebug() << "Hello Qt World!";
return 0;
}

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I compiled any of these file as like:
\qmake -project
......
\qmake
......
\make
......

There is no any error ,but when I run the helloworld.exe,there is no out !!!???
why!

Is there any bug with QT?!