将 C++ 与 Android ndk/jni 一起使用 [英] Use C++ with Android ndk/jni

问题描述

所有 ndk 示例仅使用在标头中声明为 extern 并在 cpp 文件中定义的基本 C 函数.然后在包含jni回调的C文件中包含头文件后，一切正常.

All the ndk samples only make use of basic C functions declared as extern in the header and defined in the cpp file. Then after including the header file in the C file containing the jni callback, everything works fine.

是否可以在 android ndk 中使用 C++ 类?我的应用程序不会是原生活动，它仍然会有一个重要的 java 部分，但它会调用原生 C 代码进行 CPU 密集型计算(已经用 C++ 编写，带有类和其他 C++ 内容).

Is it possible to use C++ classes with the android ndk? My application is not going to be a native activity, it will still have an important java part but it will call native C code for CPU-intensive computation (already written in C++, with classes and other C++ stuff).

这是我现在的 hello-world 结构:

Here is my hello-world like strcuture for now:

文件first.h"

#ifndef FIRST_H
#define FIRST_H

class Test
{};

#endif /* FIRST_H */

文件second.cpp"

File "second.cpp"

#include <jni.h>
#include "first.h"

#ifdef __cplusplus
extern "C" {
#endif

jint Java_com_example_twolibs_TwoLibs_add( JNIEnv*  env,
                                      jobject  this,
                                      jint     x,
                                      jint     y )
{
    Test t;
    return 0;
}

#ifdef __cplusplus
}
#endif

最后是 Android.mk

And finally Android.mk

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := libtwolib-second
LOCAL_SRC_FILES := second.cpp

include $(BUILD_SHARED_LIBRARY)

相当基本，但无法编译.在 .c 文件中打开 second.cpp 在包含头文件时会引发错误，我猜这是因为它不是 C++ 文件.

Pretty basic but that does not compile. Turning second.cpp in a .c file raises an error when including the header file, I guess this is because it is not a C++ file.

error: expected '=', ',', ';', 'asm' or '__attribute__' before 'Test'

将其设为 .cpp 会引发以下错误:

Making it .cpp raises the following error:

make: *** No rule to make target `/cygdrive/c/android-ndk-r5c/samples/twolibs/jni/second.c', needed by `/cygdrive/c/android-ndk-r5c/samples/two-libs/obj/local/armeabi/objs/twolib-second/second.o'.  Stop.

知道如何编译那个东西吗?

Any idea how I can make that thing compile?

谢谢

推荐答案

可以使用 C++ 和 NDK，但 C++ 代码的文件必须具有 .cpp 扩展名.

You can use C++ with NDK, but files with C++ code must have .cpp extension.

来自 ANDROID-MK.html:

请注意，C++ 源文件的默认扩展名是.cpp".它是但是可以通过定义变量来指定不同的LOCAL_CPP_EXTENSION.不要忘记最初的点(即 '.cxx' 将工作，但不是'cxx').

Note that the default extension for C++ source files is '.cpp'. It is however possible to specify a different one by defining the variable LOCAL_CPP_EXTENSION. Don't forget the initial dot (i.e. '.cxx' will work, but not 'cxx').

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