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?

Abysmal

if you just want to check if you are using android you could always use c/c++ preprocessor macros to check, #if defined(__unix__) && __ANDROID__ #define PLATFORM_ANDROID #endif if you want to check the API version for android this way use do #if defined(__unix__) && __ANDROID__ #include <android/api-level.h> #if defined(__ANDROID__) && __ANDROID_API__ == 0x00000001 #defined ANDROID_API_1 #endif #endif – Alembic

Answer 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
}

Characteristically

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

@Adar please send this comment as an answer – Botheration

property_get is from cutils, which is not part of the NDK: https://mcmap.net/q/1013313/-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. – Nikolaus

@vulcanraven, updated with solution for recent Android versions – Characteristically

what can I do if the getenv returns null? – Coakley

@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 – Characteristically

Answer 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".

Adar

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/+/… – Nikolaus

Answer 3

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.

Tomekatomes

This should be at the top. – Veda

Answer 4

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;
}

Sledgehammer

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

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. – Sledgehammer

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

Answer 5

How about using AConfiguration_getSdkVersion() API?

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

Nonperformance

Where do you get the app variable from? – Nikolaus

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

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

Answer 6

#if defined(__linux__)
// Linux-based OS

#if defined(__ANDROID__)
// Android OS
#else
// other Linux-based OS
#endif

#endif

See this for reference. The caveat is that any linux system sets __linux__, and Android sets that and __ANDROID__. For windows it's _WIN32 for most use cases.~

You can also use /path/to/your/ndk/compiler -dM -E - < /dev/null to see all the flags available to you.

Plesiosaur