TTT - example CMake project
===========================

The aim of this project is to provide a simple, no-brainer cmake project with
support for catch2 testing library.


How projects (executables/libraries) are organized
--------------------------------------------------

ttt
\
 | CMakeLists.txt
 | src
 | include
 | tests
 | *sub-libraries*

*src* is the directory containing source code (cpp/header files); however
headers contained in this directory should never be exported to any other CMake
target.

*include* is the directory containing header files which are exported to other
projects and only that. This directory can be absent if this project is an
excutable-only one.

*tests* contains tests (unit/functional) for the current project.

*sub-libraries* are multiples directories containing other CMake projects.


CMakeLists.txt
--------------

This file contains the build system definitions, configurations, etc.

Multiple sections are present into this file :

* c++ standard used is explicitely forced by variables CMAKE\_CXX\_STANDARD,
  CMAKE\_CXX\_STANDARD\_REQUIRED and CMAKE\_CXX\_EXTENSIONS. Those are adding
  GLOBALY the flag -std=c++17 to this project and all sub-projects. The
  EXTENSIONS variable controls wether we want gnu++ extensions to be enabled
  (hint: don't use them unless you explicitely want one; they are not
  cross-compiler compatible).
* options allow variables to be set, and they control the build, allowing users
  to select various things (release, optimizations, tests, etc).
* add\_compile\_options is used to add compiler flags to all projects and
  sub-projects. This allows a more coherent code base.
* the end of the file should include all sub-directories necessary to compile
  your main project.


Compiler Flags
--------------

- Wall : enable all common warnings (not "all" as the name suggests), to
  prevent you from doing stupid things and catching errors early on
- Wextra : enable even more warnings (see gcc/clang man page for details on
  which flags are enabled.
- Werror : any warning will tranform in an error, preventing the build. This
  prevents dirty/bad code from being included in the code base.
- Wold-style-cast : the name is explicit ^^ it prevents (void)variable; to
  force you to use modern/safer c++ casts.
- fvisibility=hidden : specific optimization for ELF binary file. See
  [https://gcc.gnu.org/wiki/Visibility](GCC website).
- pipe : transmit compiled artifacts throught UNIX pipes, improving compile
  times.
- O0, O3, Og : optimization level.
- flto : enable link-time optimization. Can reduce binary size, loading times,
  etc.
- s : strip output executables, to reduce size and remove anything unnecessary.


Testing
-------

Tests are supported using the Catch2 header-only library, and launched using
CTest.

The ENABLE\_TESTS variable controls :

* adding the Catch2 library. This can be replaced by any other library (i.e
  gtests or others), however you are responsible for modifying tests
  declaration/implementation to match your test engine.
* call to enable\_testing().

Tests are then added in each project, and added as need arise.


Lints
-----

CMAKE\_CXX\_CLANG\_TIDY is used to specify checks that will run on all your
sub-projects, adding even more checks than g++/clang++.