Continuing our blog series "<a href="http://sandbox.arrayfire.com/tag/learning-arrayfire-from-scratch/">Learning ArrayFire from scratch</a>" today we will discuss how to set up an ArrayFire project on Linux using CMake or standard makefiles.

<!--more-->

Once you have <a class="el" href="installing.htm">installed</a> ArrayFire on your system, the next thing to do is set up your build system. On Linux, you can create ArrayFire projects using almost any editor, compiler, or build system. The only requirements are that you include the ArrayFire header directories and link with the ArrayFire library you intend to use.
<h3>The big picture</h3>
On Linux, we suggest you install ArrayFire to the <span class="lang:default decode:true  crayon-inline">/usr/local/</span>  directory so that all of the include files and libraries are part of your standard path. The installer will populate files in the following sub-directories:
<pre class="fragment">include/arrayfire.h         - Primary ArrayFire include file
include/af/*.h              - Additional include files
lib/libaf*                  - CPU, CUDA, and OpenCL libraries (.a, .so)
lib/libforge*               - Visualization library
share/ArrayFire/cmake/*     - CMake config (find) scripts
share/ArrayFire/examples/*  - All ArrayFire examples
</pre>
Because ArrayFire follows standard installation practices, you can use basically any build system to create and compile projects that use ArrayFire. Among the many possible build systems on Linux we suggest using ArrayFire with either CMake or Makefiles with CMake being our preferred build system.
<h3>Prerequisite software</h3>
To build ArrayFire projects you will need a compiler
<h4>Fedora, Centos and Redhat</h4>
Install EPEL repo (not required for Fedora)
<div class="fragment">
<div class="line">
<pre class="lang:default decode:true ">yum install epel-release
yum update</pre>
Install build dependencies

</div>
</div>
<pre class="lang:default decode:true">yum install gcc gcc-c++ cmake make</pre>
<h4><strong>Debian and Ubuntu</strong></h4>
Install common dependencies
<div class="fragment">
<div class="line">
<pre class="lang:default decode:true">apt-get install build-essential cmake cmake-curses-gui</pre>
</div>
</div>
<h3>CMake</h3>
We recommend that the CMake build system be used to create ArrayFire projects.f you are writing a new ArrayFire project in C/C++ from scratch, we suggest you grab a copy of our <a href="https://github.com/bkloppenborg/arrayfire-cmake-example">CMake Project Example</a>; however, it is useful to read the documentation below in case you need to add ArrayFire to an existing project.

As <a href="#big-picture">discussed above</a>, ArrayFire ships with a series of CMake scripts to make finding and using our library easy. The scripts will automatically find all versions of the ArrayFire library and pick the most powerful of the installed backends (typically CUDA).

First create a file called <span class="lang:default decode:true  crayon-inline ">CMakeLists.txt</span>  in your project directory:
<pre class="fragment">cd your-project-directory
touch CMakeLists.txt
</pre>
and populate it with the following code:
<pre class="fragment">FIND_PACKAGE(ArrayFire)
INCLUDE_DIRECTORIES(${ArrayFire_INCLUDE_DIRS})

... [gather source files, etc.]

# If you intend to use OpenCL, you need to find it
FIND_PACKAGE(OpenCL)
SET(EXTRA_LIBS ${CMAKE_THREAD_LIBS_INIT} ${OpenCL_LIBRARIES})

# Or if you intend to use CUDA, you need it as well as NVVM:
FIND_PACKAGE(CUDA)
FIND_PACKAGE(NVVM) # this FIND script can be found in the ArrayFire CMake example repository
SET(EXTRA_LIBS ${CMAKE_THREAD_LIBS_INIT} ${CUDA_LIBRARIES} ${NVVM_LIB})

ADD_EXECUTABLE(my_executable [list your source files here])
TARGET_LINK_LIBRARIES(my_executable ${ArrayFire_LIBRARIES} ${EXTRA_LIBS})
</pre>
where <span class="lang:default decode:true  crayon-inline ">my_executable</span>  is the name of the executable you wish to create. See the <a href="https://cmake.org/documentation/">CMake documentation</a> for more information on how to use CMake. Clearly the above code snippet precludes the use of both CUDA and OpenCL, see the <a href="https://github.com/bkloppenborg/arrayfire-cmake-example">ArrayFire CMake Example</a> for an example of how to build executables for both backends from the same CMake script.
<pre class="fragment">ArrayFire_INCLUDE_DIRS    - Location of ArrayFire's include directory.
ArrayFire_LIBRARIES       - Location of ArrayFire's libraries. 
                            This will default to a GPU backend 
                            if one is found
ArrayFire_FOUND           - True if ArrayFire has been located
</pre>
If you wish to use a specific backend, the find script also defines these variables:
<pre class="fragment">ArrayFire_CPU_FOUND         - True of the ArrayFire CPU library has been found.
ArrayFire_CPU_LIBRARIES     - Location of ArrayFire's CPU library, if found
ArrayFire_CUDA_FOUND        - True of the ArrayFire CUDA library has been found.
ArrayFire_CUDA_LIBRARIES    - Location of ArrayFire's CUDA library, if found
ArrayFire_OpenCL_FOUND      - True of the ArrayFire OpenCL library has been found.
ArrayFire_OpenCL_LIBRARIES  - Location of ArrayFire's OpenCL library, if found
ArrayFire_Unified_FOUND     - True of the ArrayFire Unified library has been found.
ArrayFire_Unified_LIBRARIES - Location of ArrayFire's Unified library, if found
</pre>
Therefore, if you wish to target a specific specific backend, simply replace <span class="lang:default decode:true  crayon-inline ">${ArrayFire_LIBRARIES}</span>  with<span class="lang:default decode:true  crayon-inline ">${ArrayFire_CPU}</span> , <span class="lang:default decode:true  crayon-inline ">${ArrayFire_OPENCL}</span> , <span class="lang:default decode:true  crayon-inline ">${ArrayFire_CUDA}</span> , or <span class="lang:default decode:true  crayon-inline ">${ArrayFire_Unified}</span>  in the<span class="lang:default decode:true  crayon-inline ">TARGET_LINK_LIBRARIES</span>  command above.

Next we need to instruct CMake to create build instructions and then compile. We suggest using CMake's out-of-source build functionality to keep your build and source files cleanly separated. To do this:
<pre class="fragment">cd your-project-directory
mkdir build
cd build
cmake ..
make
</pre>
<em>NOTE:</em> If you have installed ArrayFire to a non-standard location, CMake can still help you out. When you execute CMake specify the path to the <span class="lang:default decode:true  crayon-inline ">ArrayFireConfig*</span>  files that are found in the <span class="lang:default decode:true  crayon-inline ">share/ArrayFire/cmake</span>  subdirectory of the installation folder. For example, if ArrayFire were installed locally to <span class="lang:default decode:true  crayon-inline ">/opt/ArrayFire</span>  then you would modify the <span class="lang:default decode:true  crayon-inline ">cmake</span> command above to contain the following definition:
<pre class="fragment">cmake -DArrayFire_DIR=/opt/ArrayFire/share/ArrayFire/cmake ..
</pre>
You can also specify this information in the <span class="lang:default decode:true  crayon-inline ">ccmake</span>  command-line interface.
<h3>MakeFiles</h3>
Building ArrayFire projects with Makefiles is fairly similar to CMake except you must specify all paths and libraries manually. As with any make project, you need to specify the include path to the directory containing <span class="lang:default decode:true  crayon-inline ">arrayfire.h</span> file. This should be <span class="lang:default decode:true  crayon-inline ">-I /usr/local/include</span>  if you followed our installation instructions. Similarly, you will need to specify the path to the ArrayFire library using the <code>-L</code> option (e.g. <span class="lang:default decode:true  crayon-inline ">-L/usr/local/lib</span> ) followed by the specific ArrayFire library you wish to use using the <code>-l</code> option (for example <span class="lang:default decode:true  crayon-inline">-lafcpu</span> , <span class="lang:default decode:true  crayon-inline">-lafopencl</span> , <span class="lang:default decode:true  crayon-inline ">-lafcuda</span> , or <span class="lang:default decode:true  crayon-inline ">-laf</span>  for the CPU, OpenCL, CUDA, and unified backends respectively.

Here is a minimial example MakeFile which uses ArrayFire's CPU backend:
<pre class="fragment">LIBS=-lafcpu
LIB_PATHS=-L/usr/lib
INCLUDES=-I/usr/include
CC=g++ $(COMPILER_OPTIONS)
COMPILER_OPTIONS=-std=c++11 -g

all: main.cpp Makefile
    $(CC) main.cpp -o test $(INCLUDES) $(LIBS) $(LIB_PATHS)</pre>
&nbsp;