Cross-compile Qt-based application with external library

Question

I've got a Qt based application written in C++ and I'm using the fuzzylite 6.0 library, and I want to link it statically.

Compilation and execution work flawlessly on my Arch Linux machine. However, I also want to build for Windows. So I built the MXE toolchain and fuzzylite for Windows using MXE (MXE_TARGETS=x86_64-w64-mingw32.static).

The compilation process works fine except for a few warnings coming from the external library (I believe they use some MSVC #pragmas to disable them, but they still show up with MinGW).

However, the resulting PE executable does absolutely nothing on an x86_64 Windows machine. No errors and nothing pops up when I launch the executable.

When I compile without fuzzylite (and without fuzzylite related code), it does work which makes me think that there is a problem during the build of my app or fuzzylite, but I wasn't able to find a solution.

---

Here are the specific steps I took:

• Install MXE Qt toolchain:

  $ git clone https://github.com/mxe/mxe.git /usr/local/src/mxe
  $ cd /usr/local/src/mxe/
  $ make MXE_TARGETS=x86_64-w64-mingw32.static PREFIX=/usr/local qtbase
  

• Build fuzzylite:

  I modified build.sh to use the MXE version of cmake after reading this answer, as it automatically use an appropriate toolchain file for Windows.

  $ git clone https://github.com/fuzzylite/fuzzylite.git /usr/local/src/fuzzylite
  $ cd /usr/local/src/fuzzylite/fuzzylite
  $ sed -i 's/cmake\b/\/usr\/local\/bin\/x86_64-w64-mingw32.static-cmake/g' build.sh
  $ /usr/local/src/fuzzylite/fuzzylite/build.sh all
  

  fuzzylite also has a build.bat file but I believe it can only be executed inside a Windows environment.

• Install fuzzylite:

  $ cp /usr/local/src/fuzzylite/fuzzylite/release/bin/lib* /usr/local/lib/release/
  $ cp /usr/local/src/fuzzylite/fuzzylite/debug/bin/lib* /usr/local/lib/debug/
  

• Build the application:

  $ x86_64-w64-mingw32.static-qmake-qt5
  $ make
  

---

Here is my .pro file (the project is called code):

#-------------------------------------------------
#
# Project created by QtCreator 2018-11-19T08:47:31
#
#-------------------------------------------------

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = code
TEMPLATE = app

# The following define makes your compiler emit warnings if you use
# any feature of Qt which has been marked as 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 you use 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

CONFIG += c++11

SOURCES += \
        main.cpp \
        mainwindow.cpp \
        analyzer.cpp \
        overlay.cpp \
        ridgeendingengine.cpp \
        minutiaengine.cpp \
        reversetrapezoid.cpp

HEADERS += \
        mainwindow.hpp \
        analyzer.hpp \
        overlay.hpp \
        ridgeendingengine.hpp \
        minutiaengine.hpp \
        reversetrapezoid.hpp

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

win32:CONFIG(release, debug|release): LIBS += -L/usr/local/lib/release/ -lfuzzylite-static
else:win32:CONFIG(debug, debug|release): LIBS += -L/usr/local/lib/debug/ -lfuzzylite-static
else:unix: LIBS += -L/usr/local/lib/ -lfuzzylite-static

INCLUDEPATH += /usr/local/include
DEPENDPATH += /usr/local/include

win32-g++:CONFIG(release, debug|release): PRE_TARGETDEPS += /usr/local/lib/release/libfuzzylite-static.a
else:win32-g++:CONFIG(debug, debug|release): PRE_TARGETDEPS += /usr/local/lib/debug/libfuzzylite-static.a
else:win32:!win32-g++:CONFIG(release, debug|release): PRE_TARGETDEPS += /usr/local/lib/release/fuzzylite-static.lib
else:win32:!win32-g++:CONFIG(debug, debug|release): PRE_TARGETDEPS += /usr/local/lib/debug/fuzzylite-static.lib
else:unix: PRE_TARGETDEPS += /usr/local/lib/libfuzzylite-static.a

A sample of the warnings generated during the build of both fuzzylite and my application:

In file included from /usr/local/src/fuzzylite/fuzzylite/./fl/Headers.h:33:0,
                 from /usr/local/src/fuzzylite/fuzzylite/src/main.cpp:17:
/usr/local/src/fuzzylite/fuzzylite/./fl/Exception.h:45:0: warning: ignoring #pragma warning  [-Wunknown-pragmas]
 #pragma warning (push)
 ^
/usr/local/src/fuzzylite/fuzzylite/./fl/Exception.h:46:0: warning: ignoring #pragma warning  [-Wunknown-pragmas]
 #pragma warning (disable:4275)
 ^
/usr/local/src/fuzzylite/fuzzylite/./fl/Exception.h:51:0: warning: ignoring #pragma warning  [-Wunknown-pragmas]
 #pragma warning (pop)
 ^

In file included from /usr/local/src/fuzzylite/fuzzylite/./fl/term/Term.h:22:0,
                 from /usr/local/src/fuzzylite/fuzzylite/./fl/factory/ConstructionFactory.h:119,
                 from /usr/local/src/fuzzylite/fuzzylite/./fl/factory/ActivationFactory.h:22,
                 from /usr/local/src/fuzzylite/fuzzylite/./fl/Headers.h:55,
                 from /usr/local/src/fuzzylite/fuzzylite/src/main.cpp:17:
/usr/local/src/fuzzylite/fuzzylite/./fl/Operation.h:993:24: warning: inline function 'static std::__cxx11::string fl::Operation::str(T, int, std::ios_base::fmtflags) [with T = const std::__cxx11::basic_string<char>&; std::__cxx11::string = std::__cxx11::basic_string<char>; std::ios_base::fmtflags = std::_Ios_Fmtflags]' declared as  dllimport: attribute ignored [-Wattributes]
     inline std::string Operation::str(const std::string& x, int decimals,
                        ^
/usr/local/src/fuzzylite/fuzzylite/./fl/Operation.h:1012:24: warning: inline function 'static std::__cxx11::string fl::Operation::join(const std::vector<T>&, const string&) [with T = std::__cxx11::basic_string<char>; std::__cxx11::string = std::__cxx11::basic_string<char>]' declared as  dllimport: attribute ignored [-Wattributes]
     inline std::string Operation::join(const std::vector<std::string>& x,
                        ^
/usr/local/src/fuzzylite/fuzzylite/./fl/Operation.h:1038:24: warning: inline function 'static std::__cxx11::string fl::Operation::join(int, const string&, T, ...) [with T = float; std::__cxx11::string = std::__cxx11::basic_string<char>]' declared as  dllimport: attribute ignored [-Wattributes]
     inline std::string Operation::join(int items, const std::string& separator,
                        ^
/usr/local/src/fuzzylite/fuzzylite/./fl/Operation.h:1054:24: warning: inline function 'static std::__cxx11::string fl::Operation::join(int, const string&, T, ...) [with T = const char*; std::__cxx11::string = std::__cxx11::basic_string<char>]' declared as  dllimport: attribute ignored [-Wattributes]
     inline std::string Operation::join(int items, const std::string& separator, const char* first, ...) {
                        ^