Qt C++ LNK2019: unresolved external symbol using QNetworkAccessManager - c++

Question

I am trying to run a simple piece of code using the documentation provided here https://doc.qt.io/qt-5/qnetworkaccessmanager.html. I am using Qt Creator with MSVC2017 64-bit Kit on Windows 10. My knowledge of C++ and Classes is very basic.
The code gives linker errors I don't know why. I have tried cleaning and re-building again but no success. Any help would be appreciated. Thanks!
I create a new project in Qt Creator with mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QtNetwork/QNetworkAccessManager>
#include <QtNetwork/QNetworkReply>
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();
void replyFinished(QNetworkReply *reply);
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
And then add these lines in mainwindow.cpp and compile.
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
QNetworkAccessManager *manager = new QNetworkAccessManager(this);
connect(manager, &QNetworkAccessManager::finished,
this, &MainWindow::replyFinished);
manager->get(QNetworkRequest(QUrl("http://qt-project.org")));
}
void MainWindow::replyFinished(QNetworkReply *reply)
{
//
}
I get linker errors at the output when I compile using MSVC2017 64-bit Kit. The issue is same if I use a different Kit (MinGW).
Here's my .pro file :
QT += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
CONFIG += c++11
# The following define makes your compiler emit warnings if you use
# any Qt feature that has been marked deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS
# You can also make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000 # disables all the APIs deprecated before Qt 6.0.0
SOURCES += \
main.cpp \
mainwindow.cpp
HEADERS += \
mainwindow.h
FORMS += \
mainwindow.ui
# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target
Here's the compiler output:
12:52:23: Running steps for project Proj2...
12:52:23: Configuration unchanged, skipping qmake step.
12:52:23: Starting: "C:\Qt\Tools\QtCreator\bin\jom.exe"
C:\Qt\Tools\QtCreator\bin\jom.exe -f Makefile.Debug
link /NOLOGO /DYNAMICBASE /NXCOMPAT /DEBUG /SUBSYSTEM:WINDOWS "/MANIFESTDEPENDENCY:type='win32' name='Microsoft.Windows.Common-Controls' version='6.0.0.0' publicKeyToken='6595b64144ccf1df' language='*' processorArchitecture='*'" /MANIFEST:embed /OUT:debug\Proj2.exe #C:\Users\HP\AppData\Local\Temp\Proj2.exe.7376.15.jom
mainwindow.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: __cdecl QNetworkRequest::QNetworkRequest(class QUrl const &)" (__imp_??0QNetworkRequest##QEAA#AEBVQUrl###Z) referenced in function "public: __cdecl MainWindow::MainWindow(class QWidget *)" (??0MainWindow##QEAA#PEAVQWidget###Z)
mainwindow.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: __cdecl QNetworkRequest::~QNetworkRequest(void)" (__imp_??1QNetworkRequest##QEAA#XZ) referenced in function "public: __cdecl MainWindow::MainWindow(class QWidget *)" (??0MainWindow##QEAA#PEAVQWidget###Z)
mainwindow.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: __cdecl QNetworkAccessManager::QNetworkAccessManager(class QObject *)" (__imp_??0QNetworkAccessManager##QEAA#PEAVQObject###Z) referenced in function "public: __cdecl MainWindow::MainWindow(class QWidget *)" (??0MainWindow##QEAA#PEAVQWidget###Z)
mainwindow.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: virtual __cdecl QNetworkAccessManager::~QNetworkAccessManager(void)" (__imp_??1QNetworkAccessManager##UEAA#XZ) referenced in function "public: virtual void * __cdecl QNetworkAccessManager::`scalar deleting destructor'(unsigned int)" (??_GQNetworkAccessManager##UEAAPEAXI#Z)
mainwindow.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: class QNetworkReply * __cdecl QNetworkAccessManager::get(class QNetworkRequest const &)" (__imp_?get#QNetworkAccessManager##QEAAPEAVQNetworkReply##AEBVQNetworkRequest###Z) referenced in function "public: __cdecl MainWindow::MainWindow(class QWidget *)" (??0MainWindow##QEAA#PEAVQWidget###Z)
mainwindow.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: void __cdecl QNetworkAccessManager::finished(class QNetworkReply *)" (__imp_?finished#QNetworkAccessManager##QEAAXPEAVQNetworkReply###Z) referenced in function "public: __cdecl MainWindow::MainWindow(class QWidget *)" (??0MainWindow##QEAA#PEAVQWidget###Z)
mainwindow.obj : error LNK2001: unresolved external symbol "protected: virtual class QNetworkReply * __cdecl QNetworkAccessManager::createRequest(enum QNetworkAccessManager::Operation,class QNetworkRequest const &,class QIODevice *)" (?createRequest#QNetworkAccessManager##MEAAPEAVQNetworkReply##W4Operation#1#AEBVQNetworkRequest##PEAVQIODevice###Z)
mainwindow.obj : error LNK2001: unresolved external symbol "public: virtual struct QMetaObject const * __cdecl QNetworkAccessManager::metaObject(void)const " (?metaObject#QNetworkAccessManager##UEBAPEBUQMetaObject##XZ)
mainwindow.obj : error LNK2001: unresolved external symbol "public: virtual int __cdecl QNetworkAccessManager::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall#QNetworkAccessManager##UEAAHW4Call#QMetaObject##HPEAPEAX#Z)
mainwindow.obj : error LNK2001: unresolved external symbol "public: virtual void * __cdecl QNetworkAccessManager::qt_metacast(char const *)" (?qt_metacast#QNetworkAccessManager##UEAAPEAXPEBD#Z)
mainwindow.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: static struct QMetaObject const QNetworkAccessManager::staticMetaObject" (__imp_?staticMetaObject#QNetworkAccessManager##2UQMetaObject##B)
Hint on symbols that are defined and could potentially match:
"__declspec(dllimport) public: static struct QMetaObject const QMainWindow::staticMetaObject" (__imp_?staticMetaObject#QMainWindow##2UQMetaObject##B)
mainwindow.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: static struct QMetaObject const QNetworkReply::staticMetaObject" (__imp_?staticMetaObject#QNetworkReply##2UQMetaObject##B)
Hint on symbols that are defined and could potentially match:
"__declspec(dllimport) public: static struct QMetaObject const QMainWindow::staticMetaObject" (__imp_?staticMetaObject#QMainWindow##2UQMetaObject##B)
debug\Proj2.exe : fatal error LNK1120: 12 unresolved externals

Answer 1

Your .pro file lacks network module import. Change first line to add network library.
QT += core gui network
You can see this from the documentation, it says there
qmake: QT += network