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Developing NEST with Eclipse

These instructions are based on Eclipse Mars (4.5). They are based on earlier instructions by Thomas Heiberg.

Installing Eclipse


You have to have a Java Development Kit (JDK) v. 1.7.0 (Java 7) or later installed. Just a Java Runtime Environment (JRE) is not enough.

You can download the JDK from Oracle’s JDK8 Download Page.

Debugger under OSX

Under OSX, you need to install gdb to be able to debug NEST with Eclipse, since Eclipse does not support lldb (yet). For installation instructions, see


From the Eclipse downloads page, download either the Eclipse IDE for C/C++ Developers or the Eclipse Installer and use it to install the C/C++ IDE.

Under OSX, always download the 64-bit version. Under Windows or Linux, download the version that fits your operating system.


In this document, I assume that you collect all your Eclipse projects in a single workspace, located at $HOME/eclipse/workspace. This will keep most Eclipse-generated files out of your code directories, reducing clutter there. But you can place your workspace anywhere.


Once you have installed and started Eclipse, go to Help > Eclipse Marketplace and install the PyDev extension, then restart Eclipse.

Once PyDev is installed, open the Eclipse preferences, go to PyDev > Interpreters > Python Interpreter and configure your interpreter. You can try Advance Auto-Config, but this will often not detect the correct Python interpreter. In that case, choose New ... and browse to the executable of your Python interpreter, e.g., $HOME/anaconda/bin/python2.7.

You need to repeat this step for each new workspace you enter.


CppStyle is a source-code formatter based on clang-format. You can install it from the Eclipse Marketplace in the same way as PyDev; remember to restart Eclipse.

Then, open Eclipse preferences, go to CppStyle and enter the path to your clang-format executable; remember that NEST code formatting uses clang-format version 3.6, so you should link to an executable for that version.

You also need to create a symbolic link from your Eclipse workspace directory to $NEST_ROOT/src/.clang-format for clang-format to find the file with the code formatting rules.

General settings in Eclipse

  1. Open Eclipse preferences and go to General > Editors > Text Editors
  2. Set the following
    • Displayed tab width to 2
    • Insert spaces for tabs checked
    • Show print margin checked and colum set to 79

Directory Structure for NEST

We discuss here some ideas on how to organize NEST source code, build and install directories. This applies even if you do not work with Eclipse.

We assume that all directories discussed here live in directory $NEST_ROOT.

$NEST_ROOT should have a single directory for source code, $NEST_ROOT/src. When working with different branches, you switch branches inside the src directory.

For each NEST build configuration, you then need a separate build directory. A build configuration here means any particular combination of a source code branch and configure options, e.g., compilation with or without MPI or with or without debugging support. Placing the install directory for a given build configuration inside the build directory reduces clutter.

A typical set of build directories could then look like this

Directory Purpose
bld_master_nompi production version for laptop, only compiled from master
bld_fixes_nompi testing code in branches for small fixes
bld_fixes_mpi testing code in branches for small fixes with MPI
bld_debug_nompi for debugging

If you have longer-running branches for major changes, you may want to create one or more bld_ directories for this branch in addition, so that you can always “hop into” work on that branch without having to recompile much code.

Setting up NEST with Eclipse


You should configure NEST as usual. In this document, we will first set up the NEST production build bld_master_nompi. Handling further configurations will be described in a later section.

We thus assume the following directory layout:

$NEST_ROOT/src                          # source code
$NEST_ROOT/bld_master_nompi             # build directory
$NEST_ROOT/bld_master_nompi/install     # install directory

You should configure, build and install NEST manually once (note that I want to build NEST with gcc 6.x from Homebrew, therefore the -DCMAKE_C_COMPILER=gcc-6 -DCMAKE_CXX_COMPILER=g++-6 arguments to cmake; NB: Make sure that you have checked out the master branch in the src directory):

cd $NEST_ROOT/bld_master_nompi
cmake -DCMAKE_INSTALL_PREFIX=$NEST_ROOT/bld_master_nompi/install -DCMAKE_C_COMPILER=gcc-5 -DCMAKE_CXX_COMPILER=g++-5 -Dwith-debug=ON ../src
make -j4
make install
make installcheck

Note: With cmake you can also generate the Eclipse project files yourself by adding the option -G "Eclipse CDT4 - Unix Makefiles". The following section assumes, that you do not use this option.

Project setup

  1. File > New > Makefile project with existing code
  2. Choose an arbitrary project name
  3. Browse to the $NEST_ROOT/src directory
  4. Keep C and C++ checked
  5. Choose GNU Autotools Toolchain for indexer settings.
  6. Click Finish

The indexer will scan the code, this may take a while.

To make Eclipse aware of configuration-dependent settings, especially include guards such as HAVE_GSL, we need to add header files from the build directory. To this end, select the project in the project browser and chooseProperties from the context menu. Then

  1. go to C/C++ General > Paths and Symbols
  2. choose Includes tab and there GNU C
  3. click Add
  4. check off for Add to all languages
  5. click File system ... and select the $NEST_ROOT/bld_master_nompi/libnestutil directory
  6. add the $NEST_ROOT/bld_master_nompi/nest directory in the same way
  7. rebuild the index when Eclipse suggest it or by choosing Index > Rebuild from the context menu on the project.

To enable code formatting with clang-format via CppStyle, open the Properties window for the project and go to C/C++ General > Formatter, enable project specific settings, choose CppStyle as Code Formatter. Source > Format will now format source code according to the .clang-format file shipped with NEST.

Finally, we need to tell Eclipse about the build path.

  1. From the project context menu, choose Build configurations > Manage .... Rename the Build GNU build configuration to according to the build directory (helps keeping an overview later), in our case bld_master_nompi.
  2. Choose the project in the project browser, then Properties from the context menu.
  3. Go to C/C++ Build
  4. It should show thebld_master_nompi (or whatever name you chose) as active configuration.
  5. Then, in the Build location section of the C/C++ Build window, click File system ..., then choose $NEST_ROOT/bld_master_nompi.
  6. If you want to build in parallel, remove the check for Use default build command and enter make -j4 as build command (replace 4 with a suitable number for your computer).

Finally, we need to amend the search path for tools Eclipse uses. In the project properties browser,

  1. go to C/C++ Build > Enviroment
  2. click Select ... and choose PATH
  3. select PATH in the variables list and click Edit ...
  4. prepend to the path
    1. /usr/local/bin: if you use Homebrew
    2. /opt/local/bin: if you use MacPorts

You can now build the project by choosing Build project from the context menu.

To install or run the testsuite, you should add additional make targets:

  1. Go to the Context Menu of the project
  2. Choose Make Targets > Create ... and add a target, e.g. install by entering this as the target name.
  3. Remove the check for Run all project builders.
  4. You should create targets
    • all (builds nest)
    • install (installs nest, including tests and help)
    • install-exec (installs compiled code and Python, but not SLI code, tests, or help; faster if you only changed C++ or Python files)
    • installcheck (runs the testsuite)
  5. You can run the targets by choosing Make Targets > Build ... from the Context Menu.

See also https://wiki.eclipse.org/CDT/Autotools/User_Guide.

Running NEST from Eclipse

To run NEST within Eclipse,

  1. go to the project properties browser
  2. select Run/Debug Settings
  3. select NEST Build (GNU) and click Edit ...
  4. rename to run_master_nompi
  5. under C/C++ Application click Browse ... and select $NEST_ROOT/bld_master_nompi/ins/bin/nest
  6. select Disable auto build (because that only builds, but does not install)

You can now run NEST by clicking the “Play” button. Input is echoed in a slightly funny way in the build-in console, but NEST works fine. You need to quit NEST with the quit command, Ctrl-D does not seem to work (made my machine hang totally on one occasion).

Running PyNEST from Eclipse

To be written.

Multiple build directories and configurations

We have little experience with multiple build directories yet, so take this with a pinch of salt and let us know about your experiences! See above for a general suggestion on how to organize build directories.

For the example here, we set up a bld_fixes_mpi build directory and then add the corresponding build and run configuration in Eclipse. In general, you need to set up one build and one run configuration for each build directory you create.

Configuring and additional build directory

Create and configure the build directory as usual and build and install NEST once (do not use the MPI compiler wrappers for cmake, as it will figure out the correct options itself).

mkdir bld_fixes_mpi
cd bld_fixes_mpi
cmake -DCMAKE_INSTALL_PREFIX=$NEST_ROOT/bld_fixes_mpi/install -DCMAKE_C_COMPILER=gcc-5 -DCMAKE_CXX_COMPILER=g++-5 -Dwith-debug=ON -Dwith-mpi=ON ../src
make -j4
make install
make installcheck

Then, in Eclipse

  1. In the project context menu, choose Build configurations > Manage ... and then New ...
  2. Choose a name, preferably the same as the build directory, here bld_fixes_mpi and choose to copy settings from an existing configuration.
  3. In the context menu, choose Build configurations > Set Active and select you new configuration.
  4. Choose Properties from the context menu and go to C/C++ General > Path and Symbols. Delete the include directories listed (for C and C++) and add the libnestutil and nest directories from the build directory, rebuild the index when Eclipse suggest it (deleting and adding paths is easier than editing them, because with the Add to all languages option you only need to add each path once).
  5. In the Properties window go to C/C++ Build, choose the Builder Settings tab and then under “Build location” click File system ... and select the build directory for this configuration, e.g., $NEST_ROOT/bld_fixes_mpi.
  6. In the Properties window, go to Run/Debug Settings, select an existing configuraton and click Duplicate, then select the new configuration and choose Edit.
  7. Edit the name of the configuration, e.g. to run_fixes_mpi and the path to the C/C++ Application. If you have not built this configuration yet, you will get a warning; ignore it.

Building and running with multiple configurations

  • You select the active configuration from the project context menu via Build Configurations > Set Active .
  • To build a different configuration directly, you can also click on the little triangle next to the hammer icon and select the configuration you want to build.

A build just runs make. If you want to do more (install, run the tests), you need to select one of the make targets from the context menu via Make Targets > Build ...; in this case, you will always run the active build configuration.

When running a new configuration for the first time,

  • either click on the triangle next to the “play” button, choose Run configurations ..., select the configuration you want to run and click Run
  • or go to the same menu via the context menu Run as ... > Run configurations ....

Afterwards, you can select the run configuration by clicking on the little triangle next to the play button.

Debugging in Eclipse

This section is very preliminary.

  1. Create a build directory and configure NEST with the --with-debug switch, then add a corresponding configuration in Eclipse as described above.
  2. Remember to also create a run configuration. Then, click the triangle next to the Bug to start debugging, choosing your debug run configuration.
  3. Eclipse stops the debugger on entry to main, you probably want to click Resume here.

NB: At present, I am not able to get any variable values out in gdb. This seems to be a gdb problem, I also have this problem with gdb on the command line. So on the Mac we may have to wait until Eclipse support lldb.