CMake Basics

CMake is a cross-platform build-generator tool. CMake does not build the project, it generates the files needed by your build tool (GNU make, Visual Studio, etc) for building HPX.

In general, the HPX CMake scripts try to adhere to the general cmake policies on how to write CMake based projects.

Basic CMake Usage

This section explains basic aspects of CMake, mostly for explaining those options which you may need on your day-to-day usage.

CMake comes with extensive documentation in the form of html files and on the cmake executable itself. Execute cmake --help for further help options.

CMake requires to know for which build tool it shall generate files (GNU make, Visual Studio, Xcode, etc). If not specified on the command line, it tries to guess it based on you environment. Once identified the build tool, CMake uses the corresponding Generator for creating files for your build tool. You can explicitly specify the generator with the command line option -G "Name of the generator". For knowing the available generators on your platform, execute:

cmake --help

This will list the generator names at the end of the help text. Generator names are case-sensitive. Example:

cmake -G "Visual Studio 9 2008" path/to/hpx

For a given development platform there can be more than one adequate generator. If you use Visual Studio "NMake Makefiles" is a generator you can use for building with NMake. By default, CMake chooses the more specific generator supported by your development environment. If you want an alternative generator, you must tell this to CMake with the -G option.

Quick Start

We use here the command-line, non-interactive CMake interface.

Download and install CMake here: CMake Downloads. Version 2.8 is the minimally required version for HPX.
Open a shell. Your development tools must be reachable from this shell through the PATH environment variable.
Create a directory for containing the build. It is not supported to build HPX on the source directory. cd to this directory:
```
mkdir mybuilddir
cd mybuilddir
```
Execute this command on the shell replacing path/to/hpx/ with the path to the root of your HPX source tree:
```
cmake path/to/hpx
```

CMake will detect your development environment, perform a series of tests and will generate the files required for building HPX. CMake will use default values for all build parameters. See the CMake Variables used to configure HPX section for fine-tuning your build.

This can fail if CMake can't detect your toolset, or if it thinks that the environment is not sane enough. On this case make sure that the toolset that you intend to use is the only one reachable from the shell and that the shell itself is the correct one for you development environment. CMake will refuse to build MinGW makefiles if you have a POSIX shell reachable through the PATH environment variable, for instance. You can force CMake to use various compilers and tools. Please visit CMake Useful Variables for a detailed overview of specific CMake variables.

Options and Variables

Variables customize how the build will be generated. Options are boolean variables, with possible values ON/OFF. Options and variables are defined on the CMake command line like this:

cmake -DVARIABLE=value path/to/hpx

You can set a variable after the initial CMake invocation for changing its value. You can also undefine a variable:

cmake -UVARIABLE path/to/hpx

Variables are stored on the CMake cache. This is a file named CMakeCache.txt on the root of the build directory. Do not hand-edit it.

Variables are listed here appending its type after a colon. It is correct to write the variable and the type on the CMake command line:

cmake -DVARIABLE:TYPE=value path/to/llvm/source

CMake supports the following variable types: BOOL (options), STRING (arbitrary string), PATH (directory name), FILEPATH (file name).