main.obj : error LNK2019: unresolved external symbol public: __cdecl - c++

Question

I'm trying to write a simple class in C++ with Qt5. I can't figure out this error comes from :
main.obj : error LNK2019: unresolved external symbol "public: __cdecl ItemModel::ItemModel(class std::basic_string,class std::allocator >)" (??0ItemModel##QEAA#V?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std###Z) referenced in function main
debug\AMWS.exe : fatal error LNK1120: 1 unresolved externals
Test.pro
QT += core
QT -= gui
CONFIG += c++11
TARGET = Test
CONFIG += console
CONFIG -= app_bundle
TEMPLATE = app
HEADERS += \
main.h \
itemmodel.h
SOURCES += \
main.cpp \
itemmodel.cpp
itemmodel.h
#ifndef ITEMMODEL_H
#define ITEMMODEL_H
#include <string>
class ItemModel
{
public:
ItemModel(std::string sku);
protected:
std::string SKU;
};
#endif // ITEMMODEL_H
itemmodel.cpp
#include "itemmodel.h"
using namespace std;
ItemModel::ItemModel(string sku) : SKU(sku)
{
}
main.h
#ifndef MAIN_H
#define MAIN_H
#include <QCoreApplication>
#include <iostream>
#include "itemmodel.h"
#endif // MAIN_H
main.cpp
#include "main.h"
#include <string>
using namespace std;
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
ItemModel product("dummy");
cout << "Great!!!" << endl;
return a.exec();
}

Answer 1

Try to delete the complete build folder (Makefiles included) and recompile.
Sometime Qt apps have weird linker errors due to makefiles not being updated by qmake when they should.