Getting OS version with NDK in C

Question

I'm writing a C program which I want to execute on my Desktop running Linux and also on an Android device.
I have to make some Desktop specific things and some Android specific things.
My question is, is there a way to get the OS version in C so I can handle if the program is executed on the Desktop or on the Android device?

Solution 1

In your native code, you could use property_get(), something like this:

#include <cutils/properties.h>

// ...

int myfunction() {
    char sdk_ver_str[PROPERTY_VALUE_MAX] = "0";
    property_get("ro.build.version.sdk", sdk_ver_str, "0");
    sdk_ver = atoi(sdk_ver_str);
    // ...   
}

On desktop, property_get() should return empty string.

Note that in starting from Android 6, <cutils/properties.h> is not available in SDK, use __system_property_get as follows:

#include <sys/system_properties.h>

// ...

int myfunction() {
    char sdk_ver_str[PROPERTY_VALUE_MAX];
    if (__system_property_get("ro.build.version.sdk", sdk_ver_str)) {
        sdk_ver = atoi(sdk_ver_str);
    } else {
        // Not running on Android or SDK version is not available
        // ...
    }
    // ...   
}

You can use adb shell getprop to see all possible Android properties. But, be aware that not all of them are supported by all devices.

---

UPDATE: If you don't need OS version, but simply want to tell if your C/C++ code is running on Android, very simple way to tell is to check if environment variable ANDROID_PROPERTY_WORKSPACE exists (on Android 7 or older), or if socket /dev/socket/property_service exists (Android 8 or newer), something like this:

include <stdlib.h>
include <unistd.h>
// ...

if (getenv("ANDROID_PROPERTY_WORKSPACE")) {
    // running under Android 7 or older
} else if (access("/dev/socket/property_service", F_OK) == 0) {
    // running under Android 8 or newer
} else {
    // running on desktop
}

Solution 2

property_get() did not work for me, instead I used __system_property_get().

#include <sys/system_properties.h>

void foo() {
    char osVersion[PROP_VALUE_MAX+1];
    int osVersionLength = __system_property_get("ro.build.version.release", osVersion);
}

ro.build.version.release is a string like "6.0". You can also get ro.build.version.sdk to get the sdk level, which is a string like "23".

Solution 3

If you use the java native interface, you can use the java function to get the sdk version number, which is less dependent on android version.

int api_version( struct android_app *app ) {

    JNIEnv* env;
    app->activity->vm->AttachCurrentThread( &env, NULL );

    // VERSION is a nested class within android.os.Build (hence "$" rather than "/")
   jclass versionClass = env->FindClass("android/os/Build$VERSION" );
   jfieldID sdkIntFieldID = env->GetStaticFieldID(versionClass, "SDK_INT", "I" );

   int sdkInt = env->GetStaticIntField(versionClass, sdkIntFieldID );
   app->activity->vm->DetachCurrentThread();
   return sdkInt;
}

Solution 4

How about using AConfiguration_getSdkVersion() API?

#include <android/configuration.h>
...
auto apilevel = AConfiguration_getSdkVersion(app->config);
LOGI("Device API Level %d", apilevel);

Solution 5

NDK provide direct api to get app target sdk version or api level

android_get_device_api_level
android_get_application_target_sdk_version

See the ndk official document.

View more solutions

Comments

[weiyin]

I couldn't find <cutils/properties.h> in my NDK, but using __system_property_get from <sys/system_properties.h> worked.

[mvp]

This will give exact same result as property_get("ro.build.version.sdk"), but is much more complicated

[Matthew Grivich]

At least in my development environment (nVidia AndroidWorks, Visual Studio 2013), property_get is not readily available as it is not part of the stock android ndk. I assume I could find the source for property_get and add it to my project. However, after 10 minutes into that project, I realized JNI would do nicely. I post my answer here not to say that people can't or shouldn't use your answer, but to give people more options.

[utarid]

@weiyin please send this comment as an answer

[Simon Warta]

Where do you get the app variable from?

[Simon Warta]

I think you don't need the +1 in the char array length because __system_property_get is "copying [the] value and a \0 terminator to the provided pointer. The total bytes copied will be no greater than PROP_VALUE_MAX." android.googlesource.com/platform/bionic/+/…

[Simon Warta]

property_get is from cutils, which is not part of the NDK: stackoverflow.com/questions/17744108/cutils-not-included-in-‌​ndk I don't think cutils is meant for app development and the implementation in /system/lib/libcutils.so on your user's device could be incompatible to the <cutils/properties.h> you used at compile time.

[Mygod]

@SimonWarta I think you need to build native apps to access this android_app.

[tmm1]

Thanks for sharing. Remember to also call env->DeleteLocalRef(versionClass)

[Arto Bendiken]

developer.android.com/ndk/reference/group/…

[mvp]

@vulcanraven, updated with solution for recent Android versions

[Robert Page]

what can I do if the getenv returns null?

[mvp]

@RitobrotoGanguly: unfortunately, since this commit ANDROID_PROPERTY_WORKSPACE is not present in Android 8 (Oreo) and later. it means you have to use __system_property_get() method

[dknchris]

This should be at the top.