path: root/docs/html/sdk/ndk/overview.jd

page.title=What is the NDK?
@jd:body

 <div id="qv-wrapper">
    <div id="qv">
      <h2>In this document</h2>

      <ol>
        <li><a href="#choosing">When to Develop in Native Code</a></li>

        <li>
          <a href="#contents">Contents of the NDK</a>

          <ol>
            <li><a href="#tools">Development tools</a></li>

            <li><a href="#docs">Documentation</a></li>

            <li><a href="#samples">Sample applications</a></li>
          </ol>
        </li>

        <li><a href="#reqs">System and Software Requirements</a></li>
        
      </ol>
    </div>
  </div>

  <p>The Android NDK is a toolset that lets you embed components that make use of native code in
  your Android applications.</p>

  <p>Android applications run in the Dalvik virtual machine. The NDK allows you to implement parts
  of your applications using native-code languages such as C and C++. This can provide benefits to
  certain classes of applications, in the form of reuse of existing code and in some cases
  increased speed.</p>

  <p>The NDK provides:</p>

  <ul>
    <li>A set of tools and build files used to generate native code libraries from C and C++
    sources</li>

    <li>A way to embed the corresponding native libraries into an application package file
    (<code>.apk</code>) that can be deployed on Android devices</li>

    <li>A set of native system headers and libraries that will be supported in all future versions
    of the Android platform, starting from Android 1.5. Applications that use native activities
    must be run on Android 2.3 or later.</li>

    <li>Documentation, samples, and tutorials</li>
  </ul>

  <p>The latest release of the NDK supports these ARM instruction sets:</p>

  <ul>
    <li>ARMv5TE (including Thumb-1 instructions)</li>

    <li>ARMv7-A (including Thumb-2 and VFPv3-D16 instructions, with optional support for
    NEON/VFPv3-D32 instructions)</li>
  </ul>

  <p>Future releases of the NDK will also support:</p>

  <ul>
    <li>x86 instructions (see CPU-ARCH-ABIS.HTML for more information)</li>
  </ul>

  <p>ARMv5TE machine code will run on all ARM-based Android devices. ARMv7-A will run only on
  devices such as the Verizon Droid or Google Nexus One that have a compatible CPU. The main
  difference between the two instruction sets is that ARMv7-A supports hardware FPU, Thumb-2, and
  NEON instructions. You can target either or both of the instruction sets &mdash; ARMv5TE is the
  default, but switching to ARMv7-A is as easy as adding a single line to the application's
  <code>Application.mk</code> file, without needing to change anything else in the file. You can also build for
  both architectures at the same time and have everything stored in the final <code>.apk</code>.
  Complete information is provided in the CPU-ARCH-ABIS.HTML in the NDK package.</p>

  <p>The NDK provides stable headers for libc (the C library), libm (the Math library), OpenGL ES
  (3D graphics library), the JNI interface, and other libraries, as listed in the <a href=
  "#tools">Development Tools</a> section.</p>

  <h2 id="choosing">When to Develop in Native Code</h2>

  <p>The NDK will not benefit most applications. As a developer, you need to balance its benefits
  against its drawbacks; notably, using native code does not result in an automatic performance
  increase, but always increases application complexity. In general, you should only use native
  code if it is essential to your application, not just because you prefer to program in C/C++.</p>

  <p>Typical good candidates for the NDK are self-contained, CPU-intensive operations that don't
  allocate much memory, such as signal processing, physics simulation, and so on. Simply re-coding
  a method to run in C usually does not result in a large performance increase. When examining
  whether or not you should develop in native code, think about your requirements and see if the
  Android framework APIs provide the functionality that you need. The NDK can, however, can be an
  effective way to reuse a large corpus of existing C/C++ code.</p>

  <p>The Android framework provides two ways to use native code:</p>

  <ul>
    <li>Write your application using the Android framework and use JNI to access the APIs provided
    by the Android NDK. This technique allows you to take advantage of the convenience of the
    Android framework, but still allows you to write native code when necessary. You can install
    applications that use native code through the JNI on devices that run Android 1.5 or
    later.</li>

    <li>
      <p>Write a native activity, which allows you to potentially create an application completely in native
      code, because you can implement the lifecycle callbacks natively. The Android SDK provides
      the {@link android.app.NativeActivity} class, which is a convenience class that notifies your
      native code of any activity lifecycle callbacks (<code>onCreate()</code>, <code>onPause()</code>,
      <code>onResume()</code>, etc). You can implement the callbacks in your native code to handle
      these events when they occur. Applications that use native activities must be run on Android
      2.3 (API Level 9) or later.</p>

      <p>You cannot access features such as Services and Content Providers natively, so if you want
      to use them or any other framework API, you can still write JNI code to do so.</p>
    </li>
  </ul>

  <h2 id="contents">Contents of the NDK</h2>The NDK contains the APIs, documentation, and sample
  applications that help you write your native code.

  <h3 id="tools">Development tools</h3>

  <p>The NDK includes a set of cross-toolchains (compilers, linkers, etc..) that can generate
  native ARM binaries on Linux, OS X, and Windows (with Cygwin) platforms.</p>

  <p>It provides a set of system headers for stable native APIs that are guaranteed to be supported
  in all later releases of the platform:</p>

  <ul>
    <li>libc (C library) headers</li>

    <li>libm (math library) headers</li>

    <li>JNI interface headers</li>

    <li>libz (Zlib compression) headers</li>

    <li>liblog (Android logging) header</li>

    <li>OpenGL ES 1.1 and OpenGL ES 2.0 (3D graphics libraries) headers</li>

    <li>libjnigraphics (Pixel buffer access) header (for Android 2.2 and above).</li>

    <li>A Minimal set of headers for C++ support</li>
  </ul>

  <p>The NDK also provides a build system that lets you work efficiently with your sources, without
  having to handle the toolchain/platform/CPU/ABI details. You create very short build files to
  describe which sources to compile and which Android application will use them &mdash; the build
  system compiles the sources and places the shared libraries directly in your application
  project.</p>

  <p class="caution"><strong>Important:</strong> With the exception of the libraries listed above,
  native system libraries in the Android platform are <em>not</em> stable and may change in future
  platform versions. Your applications should <em>only</em> make use of the stable native system
  libraries provided in this NDK.</p>

  <h3 id="docs">Documentation</h3>

  <p>The NDK package includes a set of documentation that describes the capabilities of the NDK and
  how to use it to create shared libraries for your Android applications. In this release, the
  documentation is provided only in the downloadable NDK package. You can find the documentation in
  the <code>&lt;ndk&gt;/docs/</code> directory. Included are these files:</p>

  <ul>
    <li>INSTALL.HTML &mdash; describes how to install the NDK and configure it for your host
    system</li>

    <li>OVERVIEW.HTML &mdash; provides an overview of the NDK capabilities and usage</li>

    <li>ANDROID-MK.HTML &mdash; describes the use of the Android.mk file, which defines the native
    sources you want to compile</li>

    <li>APPLICATION-MK.HTML &mdash; describes the use of the Application.mk file, which describes
    the native sources required by your Android application</li>

    <li>HOWTO.HTML &mdash; information about common tasks associated with NDK development.</li>

    <li>SYSTEM-ISSUES.HTML &mdash; known issues in the Android system images that you should be
    aware of, if you are developing using the NDK.</li>

    <li>STABLE-APIS.HTML &mdash; a complete list of the stable APIs exposed by headers in the
    NDK.</li>

    <li>CPU-ARCH-ABIS.HTML &mdash; a description of supported CPU architectures and how to target
    them.</li>

    <li>CPU-FEATURES.HTML &mdash; a description of the <code>cpufeatures</code> static library that
    lets your application code detect the target device's CPU family and the optional features at
    runtime.</li>

    <li>CPU-ARM-NEON.HTML &mdash; a description of how to build with optional ARM NEON / VFPv3-D32
    instructions.</li>

    <li>CHANGES.HTML &mdash; a complete list of changes to the NDK across all releases.</li>
  </ul>

  <p>Additionally, the package includes detailed information about the "bionic" C library provided
  with the Android platform that you should be aware of, if you are developing using the NDK. You
  can find the documentation in the <code>&lt;ndk&gt;/docs/system/libc/</code> directory:</p>

  <ul>
    <li>OVERVIEW.HTML &mdash; provides an overview of the "bionic" C library and the features it
    offers.</li>
  </ul>

  <h3 id="samples">Sample applications</h3>

  <p>The NDK includes sample Android applications that illustrate how to use native code in your
  Android applications. For more information, see <a href=
  "{@docRoot}sdk/ndk/installing.html#samples">Sample Applications</a>.</p>

  <h2 id="reqs">System and Software Requirements</h2>

  <p>The sections below describe the system and software requirements for using the Android NDK, as
  well as platform compatibility considerations that affect appplications using libraries produced
  with the NDK.</p>

  <h4>The Android SDK</h4>

  <ul>
    <li>A complete Android SDK installation (including all dependencies) is required.</li>

    <li>Android 1.5 SDK or later version is required.</li>
  </ul>

  <h4>Supported operating systems</h4>

  <ul>
    <li>Windows XP (32-bit) or Vista (32- or 64-bit)</li>

    <li>Mac OS X 10.4.8 or later (x86 only)</li>

    <li>Linux (32- or 64-bit, tested on Linux Ubuntu Dapper Drake)</li>
  </ul>

  <h4>Required development tools</h4>

  <ul>
    <li>For all development platforms, GNU Make 3.81 or later is required. Earlier versions of GNU
    Make might work but have not been tested.</li>

    <li>A recent version of awk (either GNU Awk or Nawk) is also required.</li>

    <li>For Windows, <a href="http://www.cygwin.com">Cygwin</a> 1.7 or higher is required. The NDK
    will <em>not</em> work with Cygwin 1.5 installations.</li>
  </ul>

  <h4>Android platform compatibility</h4>

  <ul>
    <li>The native libraries created by the Android NDK can only be used on devices running the
    Android 1.5 platform version or later. This is due to toolchain and ABI related changes that
    make the native libraries incompatible with 1.0 and 1.1 system images.</li>

    <li>For this reason, you should use native libraries produced with the NDK in applications that
    are deployable to devices running the Android 1.5 platform version or later.</li>

    <li>To ensure compatibility, an application using a native library produced with the NDK
    <em>must</em> declare a <a href="{@docRoot}guide/topics/manifest/uses-sdk-element.html"><code>
      &lt;uses-sdk&gt;</code></a> element in its manifest file, with an
      <code>android:minSdkVersion</code> attribute value of "3" or higher. For example:
      <pre style="margin:1em;">
&lt;manifest&gt;
  ...
  &lt;uses-sdk android:minSdkVersion="3" /&gt;
  ...
&lt;/manifest&gt;
</pre>
    </li>

    <li>If you use this NDK to create a native library that uses the OpenGL ES APIs, the
    application containing the library can be deployed only to devices running the minimum platform
    versions described in the table below. To ensure compatibility, make sure that your application
    declares the proper <code>android:minSdkVersion</code> attribute value, as given in the
    table.</li>

    <li style="list-style: none; display: inline">
      <table style="margin:1em;">
        <tr>
          <th>OpenGL ES Version Used</th>

          <th>Compatible Android Platform(s)</th>

          <th>Required uses-sdk Attribute</th>
        </tr>

        <tr>
          <td>OpenGL ES 1.1</td>

          <td>Android 1.6 and higher</td>

          <td><code>android:minSdkVersion="4"</code></td>
        </tr>

        <tr>
          <td>OpenGL ES 2.0</td>

          <td>Android 2.0 and higher</td>

          <td><code>android:minSdkVersion="5"</code></td>
        </tr>
      </table>

      <p>For more information about API Level and its relationship to Android platform versions,
      see <a href="{@docRoot}guide/appendix/api-levels.html">Android API Levels</a>.</p>
    </li>

    <li>Additionally, an application using the OpenGL ES APIs should declare a
    <code>&lt;uses-feature&gt;</code> element in its manifest, with an
    <code>android:glEsVersion</code> attribute that specifies the minimum OpenGl ES version
    required by the application. This ensures that Android Market will show your application only
    to users whose devices are capable of supporting your application. For example:
      <pre style="margin:1em;">
&lt;manifest&gt;
  ...
<!-- Declare that the application uses the OpenGL ES 2.0 API and is designed
     to run only on devices that support OpenGL ES 2.0 or higher. -->
  &lt;uses-feature android:glEsVersion="0x00020000" /&gt;
  ...
&lt;/manifest&gt;
</pre>

      <p>For more information, see the <a href=
      "{@docRoot}guide/topics/manifest/uses-feature-element.html"><code>&lt;uses-feature&gt;</code></a>
      documentation.</p>
    </li>

    <li>If you use this NDK to create a native library that uses the API to access Android {@link
    android.graphics.Bitmap} pixel buffers or utilizes native activities, the application
    containing the library can be deployed only to devices running Android 2.2 (API level 8) or
    higher. To ensure compatibility, make sure that your application declares <code>&lt;uses-sdk
    android:minSdkVersion="8" /&gt;</code> attribute value in its manifest.</li>
  </ul>