Writing cross-platform applications with Git, Qt and CMake

I've been working a lot on the new fwbackups branch, where my main goal was to make it faster, more versatile and cross-platform. I decided to write it in C++ and use Qt for the interface, since when combined with CMake it would be very easy to have it compiling on all platforms. Stick the code into a git repo and you've got cross-platform building with cross-platform revision control! If you're looking for a way to setup a cross-platform application, I've listed the steps I took below:

Step 1: Install the Dependencies

Before we begin, you'll have to install a few dependencies:

Step 2: Create the git repository

Now that you have Git installed, it's time to create the Git repository which will host your project. Open up a command line and type:

  • Linux (Applications Menu > System Tools > Terminal), Unix or Mac OS X (Macintosh HD > Applications > Utilities > Terminal):

    mkdir -p ~/development/ProjectName
    cd ~/development/ProjectName
    git init
  • Microsoft Windows (Start > Run, type "cmd"):
    mkdir "My Documents"
    mkdir "My Documents\development"
    mkdir "My Documents\development\ProjectName"
    cd "My Documents\development\ProjectName"
    git init

This will initialize a git repository called ProjectName inside the "development" folder in your home. You can replace ProjectName with whatever you'd like, but just remember to replace all further instances of it in this tutorial with the same name.

If you'd like to share the project and authorize with other developers to commit to the Git repository, be sure to check out gitosis.

Step 3: Directory Layout

While it's not required, I chose to use an out-of-source build to help keep the source directories clean and keep the build files for each platform separate. Inside your newly-created ProjectName folder, create the following directory tree:

  • build/
  • build/mingw/
  • build/linux/
  • build/osx/
  • build/unix/
  • pixmaps/
  • src/
  • translations/

Step 4: Configure CMake

The last step is to configure CMake. When CMake is invoked, it reads the CMakeLists.txt file and then automatically generates Makefiles for your platform. Use this template CMakeLists.txt file and save it in the ProjectName directory created earlier:

# Name of the project
project( ProjectName )

# Essentially, just split up your project version numbers by the dot.
# These variables map version 0.0.1 of ProjectName.
set( VERSION_MAJOR "0" )
set( VERSION_MINOR "0" )
set( VERSION_PATCH "1" )

if( APPLE )
  # If we're running OS X, we need CMake 2.6.0
  cmake_minimum_required(VERSION 2.6.0)
  set( CMAKE_OSX_ARCHITECTURES "ppc;i386" )
else( APPLE )
  # Otherwise, CMake 2.4.8 is fine
  cmake_minimum_required( VERSION 2.4.8 )
endif( APPLE )

# This project requires Qt4 and Gettext
# If your project does not use Qt or Gettext, simpy remove these lines.
find_package( Qt4 REQUIRED )
find_package( Gettext REQUIRED )

# Enable all compiler warnings
add_definitions( -Wall )

# Process the "src" subdirectory
add_subdirectory(src)

If you're using gettext for translations (as many open-source projects do) then all you need to change is the ProjectName at the beginning and the version number. You'll notice that "add_subdirectory(src)" is called, so the next step is to create the CMakeLists.txt in the ProjectName/src directory:

# All cpp files go here
set(SRC_FILES
    main.cpp
    ProjectName.cpp
   )

# Headers with signal/slot definitions go here
# Remove me if not using Qt
set(MOC_HDRS
    ProjectName.h
    )

# Qt designer interface files go here
# Remove me if not using Qt
set(UI_FILES
    interface/ProjectName.ui
    )

# Qt RC files go here, uncomment if applicable
# Remove me if not using Qt
#set(RC_FILES ProjectName.qrc)

# Remove me if not using Qt
qt4_wrap_ui( UI_HDRS ${UI_FILES} )
qt4_wrap_cpp( MOC_SRCS ${MOC_HDRS} )
# If you're using Qt RC files, uncomment this too
#qt4_add_resources( RC_SRC_FILES ${RC_FILES} )
# Includes the standard Qt libraries
include( ${QT_USE_FILE} )

# Include your headers in the build and source directories
# If you need to include more directories, add them here
include_directories( ${ProjectName_BINARY_DIR}/src
                     ${ProjectName_SOURCE_DIR}/src
                     )

if( APPLE )
  # Define some settings for the Bundle
  set( MACOSX_BUNDLE_BUNDLE_NAME ProjectName )
  set( MACOSX_BUNDLE_GUI_IDENTIFIER "ProjectName" )
  set( MACOSX_BUNDLE_ICON_FILE ProjectName.icns )
  set( MACOSX_BUNDLE_INFO_STRING ""${VERSION_MAJOR}.${VERSION_MINOR}.${VERSION_PATCH}",
                                 Copyright 2008 ProjectName team" )
  set( MACOSX_BUNDLE_SHORT_VERSION_STRING "${VERSION_MAJOR}.${VERSION_MINOR}" )
  set( MACOSX_BUNDLE_LONG_VERSION_STRING "${VERSION_MAJOR}.${VERSION_MINOR}.${VERSION_PATCH}" )
  set( MACOSX_BUNDLE_BUNDLE_VERSION "${VERSION_MAJOR}.${VERSION_MINOR}.${VERSION_PATCH}" )
  set( MACOSX_BUNDLE_COPYRIGHT "(C) 2005-2008 Stewart Adam" )
  # create a bundle with an icon too!
  # If you're not using Qt, uncomment the next line and comment the line below it:
  #add_executable( ProjectName MACOSX_BUNDLE ${SRC_FILES} )
  add_executable( ProjectName MACOSX_BUNDLE ${SRC_FILES} ${MOC_SRCS} ${RC_SRC_FILES} ${UI_HDRS} )
  
  # Allows for bundle re-creation just by running "make". Also installs bundle icon
  add_custom_target( osx_bundle_dirs
    COMMAND mkdir -p ${CMAKE_CURRENT_BINARY_DIR}/ProjectName.app/Contents/Resources
    COMMAND mkdir -p ${CMAKE_CURRENT_BINARY_DIR}/ProjectName.app/Contents/MacOS
    COMMAND cp ../../../pixmaps/${MACOSX_BUNDLE_ICON_FILE}
            ${CMAKE_CURRENT_BINARY_DIR}/ProjectName.app/Contents/Resources/${MACOSX_BUNDLE_ICON_FILE}
    # Qt translations - uncomment this line when you need to install them to the bundle
    #COMMAND cp *.qm ${CMAKE_CURRENT_BINARY_DIR}/ProjectName.app/Contents/Resources/
   )
  add_dependencies( ProjectName osx_bundle_dirs )
  # This tells cmake where to place files inside the bundle
  set_source_files_properties( ${ProjectName_RESOURCES} ${ProjectName_TRANSLATIONS}
    PROPERTIES MACOSX_PACKAGE_LOCATION Resources )
else( NOT APPLE )
  # Builds a binary for windows (without cmdline showing), regular for Linux
  # If you need the cmdline showing, remove the WIN32 attribute
  
  # If you're not using Qt, uncomment the next line and comment the line below it:
  #add_executable( ProjectName WIN32 ${SRC_FILES} )
  add_executable( ProjectName WIN32 ${SRC_FILES} ${MOC_SRCS} ${RC_SRC_FILES} ${UI_HDRS} )
endif( APPLE )

# Link Qt to the executable
target_link_libraries( ProjectName ${QT_LIBRARIES} ) 

Step 5: Build the project

Now that CMake is configured, you're good to go! To build the project, run:

cd ~/development/ProjectName/build/osx
cmake . ../../
make

If you'd like to build for Unix or Linux instead of Mac OS X, change the "build/osx" to "build/unix" or "build/linux" respectively. If you're running Windows, you need to reverse the slash direction and add an additional parameter to CMake:

cd "My Documents\development\ProjectName\build\mingw"
cmake . ..\..\ -G "MinGW Makefiles"
make
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