Android Studio cmake和jni的一些坑

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1.路径

修改前CMakeLists.txt动态库配置部分

add_library( avcodec-57             SHARED             IMPORTED )set_target_properties( avcodec-57                       PROPERTIES IMPORTED_LOCATION                       libs/armeabi/libavcodec-57.so )

执行后出错

Error while executing 'D:\Android\Sdk\cmake\3.6.3155560\bin\cmake.exe' with arguments {--build E:\MyApplication2\app\.externalNativeBuild\cmake\debug\armeabi --target native-lib}ninja: error: 'libs/armeabi/libavcodec-57.so', needed by '../../../../build/intermediates/cmake/debug/obj/armeabi/libnative-lib.so', missing and no known rule to make it

在提示信息可以看出编译时的路径为

E:\MyApplication2\app\.externalNativeBuild\cmake\debug\armeabi

因此在CMakeList.txt中增加一个配置，即CMakeList.txt所在的目录

set(CURRENT_DIR ${CMAKE_SOURCE_DIR})//在Gradle Console输出信息//CMAKE_SOURCE_DIR: E:/MyApplication2/appmessage("CURRENT_DIR:" ${CMAKE_SOURCE_DIR})add_library( avcodec-57             SHARED             IMPORTED )set_target_properties( avcodec-57                       PROPERTIES IMPORTED_LOCATION                       ${CURRENT_DIR}/libs/armeabi/libavcodec-57.so )

2.使用cpp开发时的extern “C”

//file native-lib.cpp#include <jni.h>#include <string>//用extern "C"将C库的头文件和代码用｛｝括起来extern "C"{//ffmpeg使用c开发，所以头文件要用extern "C"声明#include "libavcodec/avcodec.h"jstringJava_com_jesure_myapplication_MainActivity_stringFromJNI(        JNIEnv *env,        jobject /* this */) {    char info[10000] = {0};    sprintf(info, "%s\n", avcodec_configuration());    //cpp中的JNIEnv是一级指针，在c中是二级指针    //在c中下面语句写为 return (*env)->NewStringUTF(info);    return env->NewStringUTF(info);}}

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