The First Build

Das KDevelop-Programmierhandbuch: Leitfaden zur C++-Anwendungsentwicklung für das K Desktop Environment (KDE) mit Hilfe der KDevelop-IDE in der Version 1.2
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# 3.2. The First Build

After our project is generated, we'll first make a trip through the source code to get a general understanding how the application frame works. This won't only help to get started but we'll know where to change what in later steps.

When opening the LFV (Logical File Viewer) page on the tree-view, you see some folders that already sort the project files relevant to the developer. The first two folders are "Header" and "Sources". The Header-folder therefore logically contains all header files of the project, the Sources-folder all sourcecodes. All other folders are of no interest right now, so we'll turn back here later to see what they contain.

The two folders then contain the following files:

Headers:

- kscribble.h : contains the class declaration for the class KScribbleApp.

- kscribbledoc.h : contains the class declaration for the class KScribbleDoc.

- kscribbleview.h : contains the class declaration for the class KScribbleView.

- resource.h : contains a macro collection for the menu-ID's

Sources:

- kscribble.cpp : contains the implementation of the class KScribbleApp.

- kscribbledoc.cpp : contains the implementation of the class KScribbleDoc.

- kscribbleview.cpp : contains the implementation of the class KScribbleView.

- main.cpp : contains the main() function implementation.

Before diving into the sources, we'll let KDevelop build and run our new application. To do this, select "Make" from the "Build"-menu or hit the according button on the toolbar . The output window opens from the bottom of KDevelop and lets you see what `make` does by the messages it gives us:

     1   Making all in docs
     2   make[1]: Entering directory `/home/rnolden/Tutorial/kscribble1/kscribble/docs'
     3   Making all in en
     4   make[2]: Entering directory `/home/rnolden/Tutorial/kscribble1/kscribble/docs/en'
     5   make[2]: Nothing to be done for `all'.
     6   make[2]: Leaving directory `/home/rnolden/Tutorial/kscribble1/kscribble/docs/en'
     7   make[2]: Entering directory `/home/rnolden/Tutorial/kscribble1/kscribble/docs'
     8   make[2]: Nothing to be done for `all-am'.
     9   make[2]: Leaving directory `/home/rnolden/Tutorial/kscribble1/kscribble/docs'
     10  make[1]: Leaving directory `/home/rnolden/Tutorial/kscribble1/kscribble/docs'
     11  make[1]: Entering directory `/home/rnolden/Tutorial/kscribble1/kscribble'
     12  g++ -DHAVE_CONFIG_H -I. -I. -I.. -I/opt/kde/include -I/usr/lib/qt/include  -I/usr/X11R6/include    -O0 -g -Wall  -c
         kscribbleview.cpp
     13  g++ -DHAVE_CONFIG_H -I. -I. -I.. -I/opt/kde/include -I/usr/lib/qt/include  -I/usr/X11R6/include    -O0 -g -Wall  -c
         kscribbledoc.cpp
     14  g++ -DHAVE_CONFIG_H -I. -I. -I.. -I/opt/kde/include -I/usr/lib/qt/include  -I/usr/X11R6/include    -O0 -g -Wall  -c
         kscribble.cpp
     15  g++ -DHAVE_CONFIG_H -I. -I. -I.. -I/opt/kde/include -I/usr/lib/qt/include  -I/usr/X11R6/include    -O0 -g -Wall  -c
         main.cpp
     16  /usr/bin/moc ./kscribble.h -o kscribble.moc.cpp
     17  g++ -DHAVE_CONFIG_H -I. -I. -I.. -I/opt/kde/include -I/usr/lib/qt/include  -I/usr/X11R6/include    -O0 -g -Wall  -c
         kscribble.moc.cpp
     18  /usr/bin/moc ./kscribbledoc.h -o kscribbledoc.moc.cpp
     19  g++ -DHAVE_CONFIG_H -I. -I. -I.. -I/opt/kde/include -I/usr/lib/qt/include  -I/usr/X11R6/include    -O0 -g -Wall  -c
         kscribbledoc.moc.cpp
     20  /usr/bin/moc ./kscribbleview.h -o kscribbleview.moc.cpp
     21  g++ -DHAVE_CONFIG_H -I. -I. -I.. -I/opt/kde/include -I/usr/lib/qt/include  -I/usr/X11R6/include    -O0 -g -Wall  -c
         kscribbleview.moc.cpp

     22  /bin/sh ../libtool --silent --mode=link g++  -O0 -g -Wall   -o kscribble -L/opt/kde/lib  -L/usr/X11R6/lib -rpath /opt/kde/lib
         -rpath /usr/X11R6/lib kscribbleview.o kscribbledoc.o kscribble.o main.o kscribble.moc.o kscribbledoc.moc.o kscribbleview.moc.o
         -lkfile -lkfm -lkdeui -lkdecore -lqt -lXext -lX11

     23  make[1]: Leaving directory `/home/rnolden/Tutorial/kscribble1/kscribble'

As you see, we've put line numbers in front of each line, which won't appear in your output; it just makes it easier to describe what happened during the build now. First of all, `make` works recursively. That means, it starts from the directory it is invoked in and then goes into the subdirectories first, returns and processes the next directory. Finally, the directory it was started is processed and `make` finishes. Therefore, `make` started in the main project directory containing the sources first. In line 1 and 2, you see how the `make` process goes into the `docs` directory, then into the `en` subdirectory. As there isn't anything to do, it leaves these directories until it returns to the source-directory `kscribble` in line 11. Then, the real work starts: `make` invokes the compiler, here `g++` to compile the source-file `kscribbleview.cpp`. The macro `-DHAVE&_;CONFIG&_;H` says that the file `config.h` should be used. This is a file containing macros for the specific platform and application and is located in the main project directory. The following `-I` commands add the include path where `g++` can find the includes it needs. These are the current directory, the main project directory (by `-I..`) and the include path for the KDE, Qt and X11 library header files. The directories for these include files were determined by the `configure` script and set in the Makefiles, therefore, the compiler knows where these are located. Finally, `-O0` sets the optimization to zero (no optimization), `-g` enables debugging, `-Wall` sets the compiler warnings to `all` and `-c` tells the compiler to produce an object file, so only compile the file.

This is done for the other source files of our project as well in lines 13-15. Obviously, our sources are compiled, but instead of linking the object files of the sources to the final binary, we see some other commands. In line 16, you see that the program "moc" is called to process the header file `kscribble.h`, with its output in `kscribble.moc.cpp`. Then, in line 17, this source file is compiled as well. The same happens with the other project header files until line 21. Now, as the Qt toolkit contains the signal/slot mechanism, but still stays a C++ implementation, you're using certain keywords that are not originally C++ language, such as the `signals:` and `slots:` declaration in your classes. This gives you the ability to easily allow object communication for all class objects that inherit the class `QObject`, so you can avoid the usual callback pointer functions. Therefore, the application needs the sources that implement this functionality, and that is why `moc` is called. `Moc` is the Meta Object Compiler of the Qt toolkit and builds the implementation for signals and slots mechanisms by parsing the header file and producing a source output that has to be compiled in the binary. As KDevelop projects use `automoc` to determine, which header file needs to be processed, you don't have to take care for any call on `moc` and the C++ compiler on the moc output files. Just remember the rules that make a class use the signals and slots- inheritance from `QObject` or any class that inherits `QObject` itself, inclusion of the `Q&_;OBJECT` macro (without semicolon !) at the beginning of the class declaration and the declarations for signals and slots.

Finally, your binary is built by the compiler. The output binary is called `kscribble`, the linker includes the path for the KDE and X11 libraries and links the sources against the libraries `kfile, kfm, kdeui, kdecore, qt, Xext` and `X11`. Then you're done and make exits.

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