Can I use Qt without qmake or Qt Creator?

Question

I want to program using Qt, but I don't want to use special compilers or IDE such as Qt Creator and qmake. I want to write with Kate and compile with g++.

Can I compile a program that uses Qt with g++? How do I compile it with g++?

Solution 1

Sure you can. Although it is more convenient with qmake or CMake, you can do:

CXXFLAGS += -Ipath_to_your_qt_includes
LDFLAGS += -Lpath_to_your_qt_libs

LDLIBS += -lqt-mt (for Qt3)

or

LDLIBS += -lQtCore -lQtGui (for Qt4, add what you need)

my_prog: my_prog.cpp

(in a makefile)

Update - invoking moc:

Quote from moc manpage:

Here is a useful makefile rule if you only use GNU make:

m%.cpp: %.h
        moc $< -o $@

I'd personally name the output rather %.moc.cpp (than m%.cpp). You then add the dependency of my_prog on my_prog.moc.cpp

my_prog: my_prog.cpp my_prog.moc.cpp

Similarly for uic. The situation here is more complicated, since you have to generate rules for headers and source files, and you have to add a dependency on a header file to ensure it gets generated before the sources are compiled. Something like this might work:

my_prog: my_prog.o my_prog.moc.o my_prog.ui.o
        $(CXX)  $(LDFLAGS) -o my_prog $^ $(LDLIBS)

my_prog.o: my_prog.cpp my_prog.ui.h

Solution 2

You certainly don't have to use QtCreator to write a Qt program.

You also don't have to use qmake but you are asking for trouble by not using it.

To do anything even remotely interesting in Qt you will inevitably end up subclassing QObject. All these subclasses require the Q_OBJECT macro in their definition which enables the signal/slot syntax. This syntax is not regular C++ and cannot be compiled using g++. Files containing class definitions with Q_OBJECT must be run through Qt's meta-object compiler which is called moc. This means you have to work out which files need to have moc applied to them, then run moc on them, and then compile the resulting cpp file with g++. This is the reason that Qt supplies qmake. It generates the correct rules in the Makefile for you.

Qt .pro project files are really quite straightforward to work with and I would seriously recommend that you use them. Remember, qmake is a command line tool just like g++. Also, it can actually create a skeleton project file for you by supplying the -project option so to get started you can just do

qmake -project
qmake
make

and you are done. In practice I find that the generated project file may be missing the declaration of any extra Qt libraries I might be using so you might have to add a line like

QT += opengl

if, for example, you have included something like QGLWidget.

Solution 3

Here is my makefile for any Qt project without using qmake:

#---------------------------------------------------------------------------------
# Compiler executables
#---------------------------------------------------------------------------------
CC      :=  gcc
CXX     :=  g++

#---------------------------------------------------------------------------------
# Options for code generation
#---------------------------------------------------------------------------------
DEFINES :=  -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -DQT_SHARED
CFLAGS  :=  -g -Wall $(DEFINES)
CXXFLAGS:=  $(CFLAGS)
LDFLAGS :=  -g -Wl

#---------------------------------------------------------------------------------
# Any extra libraries you wish to link with your project
#---------------------------------------------------------------------------------
LIBS    :=  -lQtGui -lQtCore -lpthread

#---------------------------------------------------------------------------------
# Some more include paths
#---------------------------------------------------------------------------------
INCPATHS:=  -I/usr/share/qt4/mkspecs/default -I/usr/include/QtGui -I/usr/include/QtCore

#---------------------------------------------------------------------------------
# Source folders and executable name
#---------------------------------------------------------------------------------
TARGET  :=  $(shell basename $(CURDIR))
BUILD   :=  build
SOURCES :=  source
INCLUDES:=  source include

#---------------------------------------------------------------------------------
# Source files
#---------------------------------------------------------------------------------
ifneq ($(BUILD),$(notdir $(CURDIR)))
#---------------------------------------------------------------------------------
export OUTPUT   :=  $(CURDIR)/$(TARGET)

export VPATH    :=  $(foreach dir,$(SOURCES),$(CURDIR)/$(dir)) \
                    $(foreach dir,$(INCLUDES),$(CURDIR)/$(dir))

CFILES      :=  $(foreach dir,$(SOURCES),$(notdir $(wildcard $(dir)/*.c)))
CPPFILES    :=  $(foreach dir,$(SOURCES),$(notdir $(wildcard $(dir)/*.cpp)))
HFILES      :=  $(foreach dir,$(INCLUDES),$(notdir $(wildcard $(dir)/*.h)))

#---------------------------------------------------------------------------------
# Use CXX for linking C++ projects, CC for standard C
#---------------------------------------------------------------------------------
ifeq ($(strip $(CPPFILES)),)
#---------------------------------------------------------------------------------
    export LD   :=  $(CC)
#---------------------------------------------------------------------------------
else
#---------------------------------------------------------------------------------
    export LD   :=  $(CXX)
#---------------------------------------------------------------------------------
endif
#---------------------------------------------------------------------------------

export OFILES   :=  $(CPPFILES:.cpp=.o) $(CFILES:.c=.o) $(HFILES:.h=.moc.o)

export INCLUDE  :=  $(foreach dir,$(INCLUDES),-I$(CURDIR)/$(dir)) $(INCPATHS)

#---------------------------------------------------------------------------------
.PHONY: $(BUILD) clean install uninstall
#------------------------------------------------------------------------------
$(BUILD):
    @[ -d $@ ] || mkdir -p $@
    @make --no-print-directory -C $(BUILD) -f $(CURDIR)/Makefile

#---------------------------------------------------------------------------------
clean:
    @echo clean ...
    @rm -fr $(BUILD) $(TARGET)

#---------------------------------------------------------------------------------
install:
    @cp -u $(TARGET) /usr/bin/$(TARGET)
    @echo installed.

#---------------------------------------------------------------------------------
uninstall:
    @rm -f /usr/bin/$(TARGET)
    @echo uninstalled.

#---------------------------------------------------------------------------------
else
#---------------------------------------------------------------------------------
# Makefile targets
#---------------------------------------------------------------------------------
all: $(OUTPUT)

#---------------------------------------------------------------------------------
$(OUTPUT): $(OFILES)
    @echo built ... $(notdir $@)
    @$(LD) $(LDFLAGS) $(OFILES) -o $@ $(LIBS)

#---------------------------------------------------------------------------------
%.o: %.c
#---------------------------------------------------------------------------------
    @echo $(notdir $<)
    @$(C) $(CFLAGS) $(INCLUDE) -c $< -o $@

#---------------------------------------------------------------------------------
%.o: %.cpp
#---------------------------------------------------------------------------------
    @echo $(notdir $<)
    @$(CXX) $(CXXFLAGS) $(INCLUDE) -c $< -o $@

#---------------------------------------------------------------------------------
%.moc.cpp: %.h
#---------------------------------------------------------------------------------
    @echo $(notdir $<)
    @moctool $< $(DEFINES) $(INCLUDE) -o $@

#---------------------------------------------------------------------------------
%.moc.o: %.moc.cpp
#---------------------------------------------------------------------------------
    @echo $(notdir $<)
    @$(CXX) $(CXXFLAGS) $(INCLUDE) -c $< -o $@

#---------------------------------------------------------------------------------
endif
#---------------------------------------------------------------------------------

Here, moctool is a simple tool that helps for non-QObject headers, here is its source code:

https://github.com/Quent42340/EasyLib/blob/master/tools/moctool/source/main.cpp

Comments

[teukkam]

Also, if you use Qt's extended syntax like signals and slots and stuff, you need to run moc manually. That's the only "mandatory" special compiler.

[Ken Bloom]

And this answer doesn't show you how to run moc (something that it sorely needs to demonstrate)

[San Jacinto]

for all intent and purpose, Qt is pretty useless without QMake. Nice answer.

[MSalters]

Actually, you can decide to use the .qpp extension for files that need moc'ing. This allows you to create a make rule (or a custom Visual Studio build rule). The generated .cpp file will be compiled normally.

[ph0t0n]

I realize this is old, but this answer is exactly what I am trying to do on my current project. However, I'm struggling with understanding a few bits of the logic. First, line 36: ifneq ($(BUILD),$(notdir $(CURDIR))) seems to check if the makefile was executed from the build directory, if not it seems to call another @make --no-print-directory -C $(BUILD) -f $(CURDIR)/Makefile on line 71. Why? Everything that occurs after the else on line 93 starting with the all: target is what I would expect, instead. I'm hoping the OP will respond...

[JBentley]

This answer is misleading. Qmake is a build tool and is independent from moc. You can successfully and easily call moc from a different build tool. I've done this in Visual Studio and SCons for example. In both its easy to have this handled transparently so that you can carry on as normal, as if moc didn't exist.

[Troubadour]

@JBentley: The answer makes it quite clear that without qmake you would have to "work out which files need to have moc applied to them, then run moc on them". I currently work at a company where we have our own build system and it calls moc without the help of qmake.

[JBentley]

@Troubadour Yes, but you also said that "you are asking for trouble by not using [qmake]", and that "I would seriously recommend that you use [.pro project files]". I didn't say that your answer was wrong, just misleading. In the context of the question, "Can I use Qt without qmake or Qt Creator?", you imply that it is difficult and/or troublesome to not use qmake. Indeed, the first commenter on the answer concludes that "Qt is pretty useless without QMake". The truth is that qmake is just one of several legitimate and highly useable alternatives.

[rfcoder89]

"Q_OBJECT...This syntax is not regular C++". It's just a macro and It's perfectly valid C++. All the macro does is declare a bunch of functions. The moc compile provides the definitions.

[Youda008]

How does one build a Debug or Release version of the project?