What is the Log API to call from an Android JNI program?

Like this:

#include <android/log.h>__android_log_write(ANDROID_LOG_ERROR, "Tag", "Error here");//Or ANDROID_LOG_INFO, ...  

Add it to your makefile like this:

LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib -llog 

Following is the code snippet that you should include in your native code.

#include <android/log.h>__android_log_write(ANDROID_LOG_ERROR, "Tag", "Error msg");//Or ANDROID_LOG_INFO, ...  

In order to use the above API, we need to link the corresponding library.

We can link a shared library in Android in 3 ways.In below 3 cases, the lines mentioned should be added in Android.mk

So here are the three ways.

#1. LOCAL_LDLIBS wayLOCAL_LDLIBS := -llog

For some reason if 1 doesnt work(it did not work for me), You can try below 2 ways

#2. LOCAL_LDFLAGS wayLOCAL_LDFLAGS := -llog#3. LOCAL_SHARED_LIBRARIES wayLOCAL_SHARED_LIBRARIES += liblog

syslog

This POSIX function also outputs to logcat.

It has the advantage of being more portable across non Android systems than __android_log_write and it automatically adds the app package to the log.

Tested with this example app: https://github.com/cirosantilli/android-cheat/tree/a080f5c370c1f06e74a8300fb4a2e93369861047/gradle/NdkSyslog the NDK source is:

#include <jni.h>#include <string>#include <syslog.h>extern "C"JNIEXPORT jstring JNICALLJava_com_cirosantilli_android_1cheat_ndksyslog_MainActivity_stringFromJNI(        JNIEnv* env,        jobject /* this */) {    syslog(LOG_CRIT, "hello syslog");    return env->NewStringUTF("Check adb logcat");}

And logcat now contains:

01-14 15:39:07.582  3633  3633 E com.cirosantilli.android_cheat.ndksyslog: hello syslog  

Tested on Android O, HiKey 960.