对‘__ android_log_print’的未定义引用

我的 make 文件有什么问题？

机器人

LOCAL_PATH := $(call my-dir)


include $(CLEAR_VARS)
LOCAL_MODULE    := foo
LOCAL_SRC_FILES := foo.c
LOCAL_EXPORT_LDLIBS := -llog
include $(BUILD_SHARED_LIBRARY)

Fo.c

#include <string.h>
#include <jni.h>
#include <android/log.h>


#define  LOG_TAG    "foo"
#define  LOGI(...)  __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)


void test() {
LOGI("test");
}

Ndk-build

foo.c:9: undefined reference to `__android_log_print'
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最佳答案

Try the following in your Android.mk file:

LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib -llog
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You need to add

LOCAL_LDLIBS := -llog

to Android.mk

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Add 

LOCAL_SHARED_LIBRARIES:= \
libbinder                       \
liblog                          \

to Android.mk

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Yes, you do need to add: LOCAL_LDLIBS := -llog as the other answers/comments have specified, however the original question did not specify if he use the jni library as: LOCAL_JNI_SHARED_LIBRARIES or as LOCAL_REQUIRED_MODULES.

I can pretty much say for sure that he has it used it as: LOCAL_REQUIRED_MODULES because of the LOCAL_EXPORT_LDLIBS := -llog in the question... unless that was added after an edit.

If you use LOCAL_REQUIRED_MODULES the shared library is installed in /system/lib instead of into the apk, because it is a required module. Therefore you will need to add LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib -llog instead of just LOCAL_LDLIBS := -llog so that when the build system is building & linking the jni shared library, it will have the -llog definitions in the correct place, available to be built under $OUT/root/system/lib. Otherwise you will continue to get the same answer, even if you only add LOCAL_LDLIBS := -llog.

So, those who commented that the -L is not needed, and the other answer was correct, they were actually incorrect in this situation.

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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 way
LOCAL_LDLIBS := -llog

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

2. LOCAL_LDFLAGS way
LOCAL_LDFLAGS := -llog


3. LOCAL_SHARED_LIBRARIES way
LOCAL_SHARED_LIBRARIES += liblog

Of course you also need to include #include <android/log.h> in your C/H file.

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If you use Android Studio and gradle, it ignores Android.mk. Add this to your build.gradle file:

android {
defaultConfig {
ndk {
moduleName "your_module_name"
ldLibs "log"
}
}
}
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This helped for me:

Android.mk

    LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)


LOCAL_MODULE    := nativeDemo
LOCAL_SRC_FILES := main.cpp
LOCAL_LDLIBS += -llog


include $(BUILD_SHARED_LIBRARY)
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In lieu with

If using the new Gradle NDK integration in Android Studio 1.3, you need to add ldLibs = ["android", "log"] to your android.ndk options – Stephen Kaiser Sep 24 at 4:20

use ldLibs.addAll(["android", "log"]) for the experimental plugin

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If you upgrade to Android Studio 2.1, above answers do not work, need use ldLibs.add() to load the lib as below:

android.ndk {
moduleName = "[the_module_name]"
ldLibs.addAll(['android', 'log'])
}
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For Android Studio 2.2 and tools.build:gradle:2.2.0 using CMake add or edit row in CMakeLists.txt:

target_link_libraries(<your_library_name>
android
log)

Thats connecting log library to yours.

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In the android studio version 2.2 and higher, there is inbuilt support for CPP when you create a new project. Also, the liblog.so is included by default. Nothing to be done apart from including the header file (android/log.h).

Checkout app/CMakeLists.txt that is created by the studio when we create new android studio project. We can see that the find_library() block and target_link_libraries() block for loglib are already present.

Also, pay attention towards the function syntax. It should be:

__android_log_print (int priority, const char *tag, const char *fmt,...);

In my case, I had left out tag parameter and ended up spending good 3 days in figuring it out.

More about CMake: Add C and C++ Code to Your Project

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In case the project you are working on has the following characteristics that differ from other 'standard' answers:

  • Not using Android Studio
  • Not using gradle and the integrated CMake
  • No Android.mk or Application.mk used at all for build
  • Using CMake and the toolchain directly (maybe your project is Qt based and without using QtCreator neither)

The following target_link_libraries usage makes it:

    find_library(ANDROID_LOG_LIB log)
target_link_libraries(${TARGET_NAME} ${ANDROID_LOG_LIB})

Being TARGET_NAMEthe name of the target to build (having set it up before with add_library or add_executable).

find_library is equally important as well as setting up the toolchain properly (use the toolchain provided by Android SDK at ANDROID_SDK_HOME/cmake/<version>/android.toolchain.cmake so it sets up CMAKE_SYSROOTwhich is used by find_ commands).

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-DCMAKE_CXX_FLAGS="-llog" helps me

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LOCAL_SHARED_LIBRARIES:= liblog to Android.mk can solve my isuue. This is because the __android_log_print is defined in libLog

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TO build with Android.bp, follow the below solution:

In this -android_log_print is defined in NDK, so for this, there is already a library is available. Use "liblog" library using shared_libs tag, take reference of the below code:

target: {
android: {
cppflags: [
"-g",
"-DUSE_LIBLOG",
],
shared_libs: ["liblog"], // can use other dependency if required.
},
darwin: {
enabled: false,
},
},
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for the case who use CMakeLists.txt to make

    externalNativeBuild {
cmake {
path 'src/main/cpp/CMakeLists.txt'
}
}

just add -llog into target_link_libraries:

target_link_libraries(<your_library_name> -llog)

the env I used are :

gradle-6.5-all.zip

classpath 'com.android.tools.build:gradle:4.1.1'

Android Studio Arctic Fox | 2020.3.1 Patch 1 Build #AI-203.7717.56.2031.7621141, built on August 8, 2021


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