# Build configuration

## Overview

To separate source code from generated files such as compiled libraries, executables, test outputs and IDE projects we create build-directories. They can be placed arbitrarily but should not be placed inside the source code. You can have as many build-directories as you like for e.g. different configurations but they will all use one source code directory. A typically directory structure:

• ogs-source-code (or simply ogs)
• build-release
• build-debug
• build-release-mpi

So just go ahead and create a build-directory along your source code directory.

## Configure with CMake

For configuring a build the open source CMake tool is used. CMakeLists.txt files replace traditional Makefiles or IDE project files. The CMake tool is run inside the build-directory with a reference to the source code-directory of the project and user-chosen options. CMake then generates based on the chosen Generator either Makefiles or project files for IDE such as Visual Studio or Eclipse inside the build directory. Also all the compiled files will be generated in this directory. This keeps the actual source code clean from intermediate files which are generated from the source code. Nothing inside the build directory will ever be version controlled because its contents can be regenerated anytime from the source code.

Because of the separation of the source code and all stuff that is generated as a part of the build process it is no problem to have several build configurations (e.g. a serial configuration and a parallelized MPI-enabled configuration) all referring to the same source code.

When you want to start over with a new configuration simply delete the build-directory, create a new one and reconfigure.

See this for a list of available options.

### Supported Visual Studio Generators

• Visual Studio 15 2017 Win64

### Note: Installation of required libraries

It is preferred to use the Conan package manager to install required third-party libraries. If Conan is installed it will automatically download either prebuilt binaries of required libraries or build them locally if a binary for your setup (operating system, compiler, ..) is not available. Check this for advanced Conan usage.

Instead of using Conan you can optionally install the required libraries manually before running CMake.

#### Multi-configuration with Conan and Visual Studio

With Conan one build directory corresponds to one configuration. If you want to have e.g. a release and a debug build you need to create two build directories. This is nothing new new to Linux / GCC user but differs to Visual Studios default behavior having just one build-folder / project with different configurations. A typical Visual Studio setup with both Release and Debug configs would be initialized as follows:

[assuming you are at the same directory where the source code directory is located]
mkdir ogs-build && cd ogs-build
mkdir debug && cd debug
cmake ../../ogs -G "Visual Studio 15 2017 Win64" -DCMAKE_BUILD_TYPE=Debug
cd .. && mkdir release && cd release
cmake ../../ogs -G "Visual Studio 15 2017 Win64" -DCMAKE_BUILD_TYPE=Release


..\..\ogs represents the relative path to the source code (please adapt if you have a different directory layout).

Please also note that in Visual Studio you have to choose the correct configuration (i.e. when opening the solution-file in the release-folder you have to switch the Visual Studio configuration to Release)!

## Option: Configure from the command line

CMake can be run from the shell by invoking the cmake command inside a build directory. You can pass any CMake variable or option with -DVARIABLE_NAME=VALUE (note the -D in front!). You can also pass the generator you want to use (e.g. Unix Makefiles or Visual Studio 15 2017 Win64-project files) with the -G parameter (to see all available generators just run cmake --help), although in most cases the appropriate generator will be chosen automatically. The last parameter to the CMake command is the path to the source code directory. A typical call would look like this:

cmake -G "Visual Studio 15 2017 Win64" -DCMAKE_BUILD_TYPE=Release ../ogs


CMake tries to autodetect your compiler so in most cases this should be enough:

cmake ../ogs


### Pro Tip: Use the Visual Studio command line

In the Start menu under Visual Studio 2017 you find a application link to x64 Native Tools Command Prompt for VS 2017. This starts a command line setup for Visual Studio 64-bit. When you run CMake commands in this command line the correct generator will be picked up automatically:

cmake ../ogs


This even allows for using Ninja as the build tool which can effectively utilize all CPU cores

### Pro Tip 2: Use a better terminal application

Use ConEmu for a better terminal experience. It automatically detects all installed terminal applications (e.g. regular Windows cmd.exe, Git shell, VS command lines, …) and feautures multiple terminals inside tabs.

## Option: Configure with a visual tool

CMake comes with a graphical tool called cmake-gui. You can find it in the Windows Start Menu. First you need to set the source and build directory. Then click Configure. Now choose the generator to be used (e.g. Visual Studio 15 2017 Win64 for Visual Studio 2015 64-bit). Now choose your desired configuration options by toggling the corresponding checkboxes. Click Configure again. Click Configure often enough until the Generate-button becomes visible. Pressing Generate will finally generate the project files inside the chosen build directory.

A more convenient way of running cmake on the command line is to use the ccmake tool. This is a shell tool but with some graphical user interface. To use it just run ccmake inside your build directory with the path to the source code (and optionally the generator you want to use) as parameter:

ccmake ../ogs


First press C to Configure. You are now presented the available configuration options. You can navigate in the list with the cursor keys and toggle / alter options with Enter. You may also press T to toggle (previously hidden) advanced options. Press C again until the Generate-option becomes visible. Press G to generate the project files and exit ccmake.

There is also the tool cmake-gui available, please see the Win-Tab for a description.