Android NDK / JNI - 对自定义头文件中定义的函数的未定义引用
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/22159183/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Android NDK / JNI - undefined reference to function defined in custom header file
提问by Pink Jazz
Using JNI, I am trying to write a native C++ method for the Android NDK that makes a call to a C function defined in a custom header file. However, I am getting an undefined reference error for my C function call.
使用 JNI，我尝试为 Android NDK 编写本机 C++ 方法，该方法调用自定义头文件中定义的 C 函数。但是，我的 C 函数调用出现未定义的引用错误。
Here is my C++ code that makes a call to the C function and returns its result to Java as a jstring:
这是我的 C++ 代码，它调用 C 函数并将其结果作为 jstring 返回给 Java：
#include <jni.h>
#include "gesture_detector.h"
JNIEXPORT jstring JNICALL Java_com_example_bmtitest_JavaAbstractionLayer_callGestureAnalysis(JNIEnv *env, jobject obj, jfloat previousX, jfloat previousY, jfloat currentX, jfloat currentY) {
return env->NewStringUTF(gestureAnalysis(previousX, previousY, currentX, currentY));
}
Here is my C function:
这是我的 C 函数：
#include <stdio.h>
#include "gesture_detector.h"
//implemented from gesture_detector.h
const char* gestureAnalysis(float previousX, float previousY, float currentX, float currentY)
{
float xOffset = currentX - previousX;
float yOffset = currentY - previousY;
if(xOffset == 0 && yOffset == 0)
{
return "TAP";
}
return "0";
}
Here is my Android.mk code:
这是我的 Android.mk 代码：
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := gestureDetector
LOCAL_SRC_FILES := gestureDetector.c NativeAbstractionLayer.cpp
LOCAL_LDLIBS := -landroid
include $(BUILD_SHARED_LIBRARY)
Apparently, it seems the function definition defined in the custom header file (gesture_detector.h) isn't being found. I think it may be a problem in my Android.mk file.
显然，似乎gesture_detector.h没有找到自定义头文件 ( ) 中定义的函数定义。我认为这可能是我的 Android.mk 文件中的问题。
Could anyone tell me what am I doing wrong here?
谁能告诉我我在这里做错了什么？
回答by Chris Stratton
An "undefined reference" error comes from the linker. Your header file only satisfied the compiler.
“未定义引用”错误来自链接器。您的头文件只满足编译器。
However, since you are mixing C and C++ your problem is likely name mangling. Basically, you need to tell the C++ compiler that the function you are trying to call was created by a C compiler rather than a C++ one, and so does not have argument type codes grafted onto its name. Right now it doesn't know that, so is trying to call the function by a C++ style decorated name which differs from the plain C name of the function the linker actually has available.
但是，由于您混合使用 C 和 C++，您的问题可能是name mangling。基本上，您需要告诉 C++ 编译器您尝试调用的函数是由 C 编译器创建的，而不是由 C++ 编译器创建的，因此没有将参数类型代码嫁接到其名称上。现在它不知道这一点，因此试图通过 C++ 风格的装饰名称调用该函数，该名称不同于链接器实际可用的函数的纯 C 名称。
Add this at the beginning of your gesture_detector.h file:
在你的gesture_detector.h 文件的开头添加：
#ifdef __cplusplus
extern "C" {
#endif
And this at the end
而这最后
#ifdef __cplusplus
}
#endif
And do a clean rebuild.
并进行干净的重建。
If your real jni glue logic is as trivial as the version presented here, switching to a C version of that could also be an option - but beware that jni syntax is different in C and C++, so you can't just change the file extension.
如果您真正的 jni 粘合逻辑与此处介绍的版本一样微不足道，那么切换到该版本的 C 版本也可能是一种选择 - 但请注意 C 和 C++ 中的 jni 语法不同，因此您不能只更改文件扩展名.
回答by Jessica Cohen
Simply doing your native C++- code between
只需在两者之间执行您的本机 C++- 代码
extern "C" {
your code
}
Is something that not always will necessarily work - as you can check here.
不一定总是有效的东西 - 您可以在此处查看。
Try adding to the Android.mk file:
尝试添加到 Android.mk 文件：
LOCAL_ALLOW_UNDEFINED_SYMBOLS := true
Here you find further infoabout it.
在这里您可以找到有关它的更多信息。
