ADB Quick Commands

I keep looking these up, so dropping them here so I don’t have to: –

This will echo all output from a Unity project; adb logcat Unity:V *:S

This will echo all output from a Unity project to a file; adb logcat Unity:V *:S -d >> output.txt

This will clear the log; adb logcat -c

This will increase the buffer size so you have more than a few seconds before your logs start to disappear; adb logcat -G 16M

Unity Build Failure, unable to update SDK

So, building on Android, I get the error; “Unity Build Failure, unable to update SDK”. The project I’m working on has been updated to a new SDK but Unity doesn’t have that SDK version installed

I used the SDK manager to update to the correct API but Unity didn’t see the change as Unity is looking at it’s ‘local’ version.

To solve this, you need to install to the specific Unity version that you’re using. Simple process; Open a CommandLine (CMD) as Administrator and type: –

“C:\Program Files\Unity\Hub\Editor\2019.3.11f1\Editor\Data\PlaybackEngines\AndroidPlayer\SDK\tools\bin\sdkmanager.bat” “platforms;android-29”

Obviously, you’ll need to adjust the Unity version and the Android SDK to what you need, but this does an in-place update of the Unity installed SDK.

Once you run that, Unity is happy again

Android: Log to console from C++

Quick example of sending debug info to the log in Android JNI C++

#include <android/log.h>

#define  LOG_TAG    "DEBUG"
#define  LOGD(...)  __android_log_print(ANDROID_LOG_DEBUG,LOG_TAG,__VA_ARGS__)
#define  LOGE(...)  __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)

// Implementation of the native method sayHello()
JNIEXPORT jstring JNICALL Java_com_ancientcoder_recog_MainActivity_sayHello(JNIEnv *env, jobject thisObj) {
    LOGD("Running C++");



Using C++ within an Android Java app

Just putting this here so I have it when I need it. I haven’t cleaned this up so it’s easy to understand, but there’s not a lot to it. Just need to have the pieces below and you’ve got everything you need to quickly and easily bold cpp into an Android Java app.

Handy links I used to figure it out: –


and here

and maybe here too

Prereqs: Android Studio 3.4.1, NDK version 16.1 (but I doubt it matters which NDK)

Files you’ll need: –

DeltaJNI.cpp: Simple cpp file with a method that returns a String to Java. Must be in a cpp directory

#include <jni.h>        // JNI header provided by JDK
#include <stdio.h>      // C Standard IO Header
#include <iostream>
#include "DeltaJNI.h"      // Generated
#include <string>

// Implementation of the native method sayHello()
JNIEXPORT jstring JNICALL Java_com_ancientcoder_recog_MainActivity_sayHello(JNIEnv *env, jobject thisObj) {

    std::string hello = "-------------------------------- Hello from C++";
    return env->NewStringUTF(hello.c_str());


DeltaJNI.h: Header file to go with the above cpp. Must be with the cpp file above in a cpp directory (see CMakeLists.txt for where I put it)

#include <jni.h>


#ifdef __cplusplus
extern "C" {

JNIEXPORT jstring JNICALL Java_com_ancientcoder_recog_MainActivity_sayHello(JNIEnv *, jobject);

#ifdef __cplusplus

#endif //RECOG_DELTA_H


CMakeLists.txt: Added to the app directory to facilitate building of the ‘native-lib’ lib

# For more information about using CMake with Android Studio, read the
# documentation:

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.4.1)

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.

add_library( # Sets the name of the library.

             # Sets the library as a shared library.

             # Provides a relative path to your source file(s).

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

find_library( # Sets the name of the path variable.

              # Specifies the name of the NDK library that
              # you want CMake to locate.
              log )

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( # Specifies the target library.

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )


build.gradle (in the ‘app’ directory): Add this at the bottom of (and inside of ) the “android {}” section:

externalNativeBuild {
    cmake {
        path "CMakeLists.txt"

…and this at the bottom of (and inside of) of the “defaultConfig {}” section: –

externalNativeBuild {
    cmake {
        cppFlags ""


Java: Add this to the java class that’s calling the C++. This loads the lib that’s built by the above CMakeLists.txt (includes the cpp file(s)) and declares a prototype for the sayHello method.

static {
    System.loadLibrary("native-lib"); // Load native library at runtime
    // This library contains a native method called sayHello()
private native String sayHello();


More Java: …and finally, add this to actually call the cpp from the java code. This will log out the returned string from the cpp code: –

Log.e(TAG, sayHello());