Problems and Solutions for using C ++ In the android JNI Environment

Preface

When testing the availability of the tinythread ++ library on different mobile platforms, several problems were encountered. Tinythread ++ is known as a thread library compatible with the c ++ 11 standard. It can be used when C ++ 11 is unavailable. In the future, C ++ 11 will become more popular and can be easily replaced.

Test status on different platforms:

• IOS: Pass. You need to rename the. M file that calls the C ++ code to the. MM file.
• WP: unknown. Not involved.
• Android: Pass. After solving the following problems.

C ++ problems in the android JNI environment:1) Error: Base operand of '-> 'has non-pointer type' _ jnienv'

The calling method of C ++ is different from that of C. Comparison:

C++:  env->NewStringUTF("JNI C++!");  C:  (*env)->NewStringUTF(env, "JNI C!");

Example:

jstringJava_com_listthrd_MainActivity_runListThrd( JNIEnv* env,                                                  jobject thiz ){  // for C++  return env->NewStringUTF("JNI C++!");  // for C//  return (*env)->NewStringUTF(env, "JNI C!");}

2) error: iostream: no such file or directory

STL library files such as iostream cannot be found, because STL is not used by ndk by default. Solution:
Create the application. mk file in the JNI directory and add the following content:

#APP_STL:=stlport_staticAPP_STL := gnustl_static

Select either of the preceding two. Gnustl is recommended because it can solve other problems. See later.
3) error: 'terminate' is not a member of 'std'

This error occurs when stlport is used. Use gnustl_static instead.
4) undefined reference to '_ cxa_end_cleanup'

This error occurs when stlport is used. Therefore, use gnustl_static instead.
5) undefined reference to '_ android_log_print'

This is a log library that is not linked to Android. Add the local_ldlibs definition to the Android. mk file as follows:

#LOCAL_EXPORT_LDLIBS := -llogLOCAL_LDLIBS := -llog

Above, local_export_ldlibs is easy to use in C language, which can be removed here.
6) Error/androidruntime (330): Fatal exception: Main
Java. Lang. unsatisfiedlinkerror...

Use the C language-style call convention to add extern before the exported JNI Function
"C" is specified, or the JNI export function is enclosed by curly arc. For example:

extern "C" {  JNIEXPORT jstring JNICALL  Java_com_listthrd_MainActivity_runListThrd( JNIEnv* env, jobject thiz )  {    // ...  }}

[Appendix]

1. tinythread ++: http://tinythreadpp.bitsnbites.eu/