How to Compile C++ Program

Geant4 libraries and its applications are written in C++. The following knowledge of C++ can be helpful to understand the compilation of Geant4 libraries and its applications.

Manual Compilation

hello.cc is a very simple C++ program. It is just a pure text file with a special suffix .cc instead of .txt. A program called compiler is needed to turn it into an executable file that can be run by a computer. In Linux, the most common compiler is GNU Compiler Collection, or GCC in short. It includes a C++ compiler, g++, the usage of which is demonstrated by the commands below (Lines started with # are comments. They are not commands). In a Mac, the default compiler is Clang. However, the same command g++ can be used to call it as well.

# compile hello.cc using GNU C++ compiler, g++
# an executable, a.out, will be generated from hello.cc
g++ hello.cc
# run a.out in current folder (./ means current folder)
./a.out
# rename output file from a.out to to hello
g++ hello.cc -o hello
# run hello in current folder (./)
./hello
# check which libraries are linked in hello in Linux
# https://unix.stackexchange.com/questions/120015
ldd hello
# the equivalent cmd of ldd in Mac is otool -L hello

g++ hello.cc does not show any output. One can request g++ to show the compilation process in detail with the verbose option -v:

g++ -v hello.cc

For people who want to learn more, the verbose output of g++ is explained in detail here: https://stackoverflow.com/a/13456065/1801749

Makefile

Compilation related commands can be written in a Makefile as recipes of compilation rules, which can be called by the make command:

# run the first rule defined in Makefile,
# which is to compile hello.cc to hello
make
# delete the generated executable file, hello
make clean
# install hello to /usr/local/bin/ folder
make install
# run hello in any folder without ./
hello
# remove /usr/local/bin/hello
make uninstall

CMake

It takes time to learn how to write a proper Makefile. The Windows operating system doesn’t even use Makefiles. Another program, CMake, can be used to generate Makefiles on Linux and Mac, or their equivalence in a Windows computer. Instructions for the cmake command are written in a file called CMakeLists.txt. They are easier to learn and more human-readable than those in a Makefile. The usage of cmake in a Linux or Mac terminal goes like

# create a folder, build/, and generate Makefiles in it
# it must be run in the same folder where CMakeLists.txt is located
cmake -B build
# get into the build folder
cd build
# use the Makefile created by CMake
make
make install

CMake provides a graphic user interface (GUI) cmake-gui for users who are not familiar with command line operations. Its installation on Windows is detailed in this YouTube tutorial. Its usage on Windows is detailed in this YouTube tutorial.

Note CMake doesn’t provide uninstall by default: https://stackoverflow.com/questions/41471620/.

Now you are ready to proceed to https://github.com/jintonic/mingle to learn how to write and compile (or build if we use the CMake terminology) a very simple C++ program that uses Geant4 libraries.