Multicore compilation with Qt 5.1 and jom on Windows 7 failed - windows

Question

I have installed Qt 5.1.1 with MinGW 4.8 and QtCreator through Qt Online installer.
I launched Qt creator and made new project (Qt application Desktop) with MainWindow class based on QMainWindow (default). It works fine and popped up a mainwindow after compilation.
However, when I used C:\Qt\Qt5.1.1\Tools\QtCreator\bin\jom.exe instead of C:\Qt\Qt5.1.1\Tools\mingw48_32\bin\mingw32-make.exe , I got some output like below.
jom 1.0.13 - empower your cores
C:\Qt\Qt5.1.1\Tools\QtCreator\bin\jom.exe -f Makefile.Release
g++ -c -pipe -fno-keep-inline-dllexport -O2 -frtti -Wall -Wextra -fexceptions -mthreads -DUNICODE -DQT_NO_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -DQT_NEEDS_QMAIN -I../foobar -I'C:/Qt/Qt5.1.1/5.1.1/mingw48_32/include' -I'C:/Qt/Qt5.1.1/5.1.1/mingw48_32/include/QtWidgets' -I'C:/Qt/Qt5.1.1/5.1.1/mingw48_32/include/QtGui' -I'C:/Qt/Qt5.1.1/5.1.1/mingw48_32/include/QtCore' -I'release' -I'.' -I'.' -I'C:/Qt/Qt5.1.1/5.1.1/mingw48_32/mkspecs/win32-g++' -o release/main.o ../foobar/main.cpp
In file included from ../foobar/main.cpp:1:0:
../foobar/mainwindow.h:4:23: fatal error: QMainWindow: No such file or directory
#include <QMainWindow>
^
compilation terminated.
jom: D:\work\build-foobar-Desktop_Qt_5_1_1_MinGW_32bit-Release\Makefile.Release [release\main.o] Error 1
jom: D:\work\build-foobar-Desktop_Qt_5_1_1_MinGW_32bit-Release\Makefile [release] Error 2
15:17:38: Process "C:\Qt\Qt5.1.1\Tools\QtCreator\bin\jom.exe" stopped with code 2
Error while building/deploying project foobar (kit: Desktop Qt 5.1.1 MinGW 32bit)
During step 'Make'
15:17:38: Elapsed time: 00:00.
My .pro is like this.
#-------------------------------------------------
#
# Project created by QtCreator 2013-09-08T15:16:13
#
#-------------------------------------------------
QT += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = foobar
TEMPLATE = app
SOURCES += main.cpp\ mainwindow.cpp
HEADERS += mainwindow.h
FORMS += mainwindow.ui
I think the line in .pro greaterThan(QT_MAJOR_VERSION, 4): QT += widgets and in the output during compilation -I'C:/Qt/Qt5.1.1/5.1.1/mingw48_32/include/QtWidgets' looks fine, but failed.
How can I compile with Qt 5.1 and jom on Windows 7 (32 bit)?
Thanks in advance.

Answer 1

Jom is a replacement of nmake and not MinGW's make.
nmake is the Visual Studio command line tool used to compile makefiles. Unfortunately that tool is using only one core (Parallel builds are handled inside Visual Studio either directly or using MSBuild, I'm not really sure). That being said, Jörg Bornemann wrote a tool called jom that sort of adds the -j command to nmake. It will allow you to compile your code using the Visual C++ compiler across different threads.
MinGW on the other end contains (amongst other things) a port of the GNU GCC compiler for Windows. Being a port, not everything that is possible to do with GCC is possible with MinGW and I guess that -jN is one of these. However, MinGW do support the option -j that will spawn as many processes as it can (beware that if you use this option, you may not be able to use your computer whilst compiling).
In your case, you probably want to use MinGW as your Qt version is compiled with it. If you want to use Visual Studio, you will have to install it but also either:
recompile Qt (and all other library dependencies) or
download the binary corresponding to the Visual Studio version you just installed.
Using jom should just work with QtCreator once this is done.

Answer 2

In my case I fixed this error by overriding system environment PATH in project settings by adding only bin path to qt, mingw and qtcreator: "E:\Qt\4.8.1\bin;E:\qt\mingw-4.4.0\bin;E:\Qt\qtcreator-4.0.0\bin" and after Run qmake and Rebuild