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Overview

The CMake tool is used to build ECMWF software. The build process takes place in two stages. First, standard build files are created from configuration files using the CMake tool; Then the platform's CMake will run some tests on the system and find out if the required software libraries and headers are available. It uses this information to create native build tools (e.g. Makefiles) are used for the actual building.Each project has a CMakeLists.txt file in every directory that controls the build process. The CMakeLists.txt file has one or more commands in the form COMMAND (args...), with COMMAND representing the name of each command and args the list of arguments, each separated by white space. current platform. Then, the actual build can take place, for example by typing 'make'.

Prerequisite

To install any ECMWF software package, the CMake tool needs to be installed on your system. On most systems this can be done through the standard package manager to install software. For further information to install CMake see

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During a build with CMake there are three different directories involved: The source dir, the build dir and the install dir.

Source directory:   (ex: tar zvxf Magics2.22.0.tar.gz in /tmp/.../src)  

The source dir is where the project's sources are stored. In This the directory to which you extract  the project's source archive. The source dir also contains the files which describe the build to CMake.

Build directory: (Ex: /tmp/.../build/magics)

This directory is where all compiler outputs are stored, which includes both object files as well as final executables and libraries. CMake also stores several files of its own here, including its cache. The location of the build dir is entirely up to you.

Install director: (Ex: /usr/local/magics)

Traditionally Unix builds are finished with a call of 'make install' which copies all relevant files from the built project you need for your everyday use to a clean place. Basically it separates all necessary files from the "garbage" which is output in the build directory. The location of the install directory is governed by the CMake cache variable CMAKE_INSTALL_PREFIX. Of course, installation is entirely optional and only takes place if you build the install target.

Generating the Makefiles with CMake

After changing into the build Magics directory, the user  has to run CMake with his own options. The command gives feedback on what requirements are fulfilled and what software is still required. Table 1 gives an overview of the different options of configure.  The default (without any options) will compile a share library only and install it in /usr/local/.

Of these, the source and build directories can be anywhere on the system. The installation directory is usually left at its default, which is /usr/local. Installing software here ensures that it is automatically available to users. It is possible to specify a different installation directory by adding -DCMAKE_INSTALL_PREFIX=/path/to/install/dir to the CMake command line.

Quick Build Example

Here is an example set of commands to set up and build a software package using default settings. More detail for a customised build is given below.

# unpack the source tarball into a temporary directory
mkdir -p /tmp/src
cd /tmp/src
tar xzvf software-version-Source.tar.gz

# configure and build in a separate directory
mkdir -p /tmp/build
cd /tmp/build
cmake /tmp/src/software-version-Source
make

The software distribution will include a small set of tests which can help ensure that the build was successful. To start the tests, type:

make test

If the tests are successful, you can install the software:

make install

General CMake options

Various options can be passed to the CMake command. The following table gives an overview of some of the general options that can be passed. Options are passed to the cmake command by prefixing them with -D, for example -DCMAKE_INSTALL_PREFIX=/path/to/dir.

The C, C++ and Fortran compilers are chosen by CMake. This can be overwritten by setting the environment variables CC, CXX and F77, before the call of to cmake, to set the preferred compiler. Further the variable CMAKE_CXX_FLAGS can be used to set compiler flags for optimisation or debugging. For example, it is recommended to use CMAKE_CXX_FLAGS="-O2 -mtune=native" or any other optimisation to compile Magics. 

Package dependent options for CMake

All ECMWF software packages share some options. The user should specify ON or OFF. If the user does not specify the option, and the default is AUTO, then CMake should try to enable it if possible, otherwise the feature is turned off. If the user explicitly specifies ON, an the feature cannot be enabled because some libraries are missing, the CMake will fail. CMake will report which options are ON and which are OFF. Please note that only features are enabled with flags, therefore, there should not be a  ENABLE_BOOST flag.

should use the same options. Here is the list of available options:

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The user will specify ON or OFF. If the user does not specify the option, and the default is AUTO, then cmake should try to enable it if possible, otherwise the feature is turned off. If the user explicitly specifies ON, an the feature cannot be enabled because some libraries are missing, the cmake must fail. cmake will report which options are ON and which are OFF. Please note that only features are enabled with flags, therefore, there should not be a  ENABLE_BOOST flag. 

Quick installation guide

This is an example list of commands needed to install Magics. It is assumed “>” is the shell prompt. The Magics version number may vary.

       >mkdir magics

      > mkdir build

>tar -xzf Magics++-2.22.0.tar.gz

>cd build 

>cmake –DCMAKE_INSTALL_PREFIX. =/path/to/where/you/install/Magics++-2.22.0

checking build system type... i686-suse-linux

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> make

> make install

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