Qt LNK2019 Error with basic Qt5 application

Question

I am trying to follow a tutorial online and learn Qt5 with QtCreator 2.6.1

However, I went and attempted to write a basic application following this tutorial and I keep getting a linking error whenever I try to build the project:

#include <QtWidgets/QApplication>
#include <QtWidgets/QLabel>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QLabel *label = new QLabel("Hello World");
    label->show();

    return app.exec();
}

Once I click "Build" I get about 50 errors resulting similar to the following:

main.obj:-1: error: LNK2019: unresolved external symbol "__declspec(dllimport) public: virtual __thiscall QApplication::~QApplication(void)" (__imp_??1QApplication@@UAE@XZ) referenced in function _main
main.obj:-1: error: LNK2019: unresolved external symbol "__declspec(dllimport) public: static int __cdecl QApplication::exec(void)" (__imp_?exec@QApplication@@SAHXZ) referenced in function _main
main.obj:-1: error: LNK2019: unresolved external symbol "__declspec(dllimport) public: void __thiscall QWidget::show(void)" (__imp_?show@QWidget@@QAEXXZ) referenced in function _main

Is there a way I can fix this by linking the libraries, etc (assuming they aren't linking correctly)? If not, is there something else I can do to try and resolve this problem?

Solution

this a linker fault that can't link object files together, first delete all the build directory, then check that this line was added to your .pro file:

QT += core gui widgets

this should work, if gets fail again, you must give more information about your compiler and their search path, plus post your .pro file content here.

Comments

[TMGunter]

I think I finally figured out what I was doing wrong. I had to add QT += widgets to my project (.pro) file. Then I read up on using qmake, ran it, and then it seemed to compile and build just fine.

[Zlatomir]

Also use the include like this: #include <QApplication> and so on, instead of: #include <QtWidgets/QApplication> it is easier (you wont need pre-processor directives for includes) to use Qt4 as target this way.

[TMGunter]

well when I was trying to #include <QApplication> it was throwing me an error in the IDE, telling me that it couldn't locate the file QApplication. QWidget/WApplication it was able to find though. After changing the .pro file though, I was able to do that.

[Zlatomir]

It's solved already, by adding QT+= widgets in the .pro file.