How to return a java string in C++ using JNI -

i need call java code , return string c++ using jni.

basically in c++ want use function "string getmystring()" obtain string java. how obtain ?

follow wrapper return std::wstring. note uses "critical string"

/** *   wraps get/releasestringcritical pairs of unicode java-string */ struct jnicriticalstring {     jnicriticalstring(jnienv *env, jstring str):         _env(env),         _str(str)     {         _pstr = _env->getstringcritical(_str, &_is_copy);     }     ~jnicriticalstring()     {         if( _pstr != null )         {             _env->releasestringcritical(_str, _pstr);         }     }     /**     *   true, if wrapped string valid - e.g. call of getstringcritical returned valid value     */     bool is_valid() const     {         return _pstr != null;     }     /** true when getstringcritical created copy instead of direct pointer */     bool is_copy() const     {         return _is_copy == jni_true;     }     /** return unicode not null terminated! string.*/     const wchar_t* c_str() const     {         return reinterpret_cast<const wchar_t*>( _pstr );     }     /** length of internal string */     jsize length() const     {         return _env->getstringlength(_str);     }     std::wstring as_string() const     {         return std::wstring(c_str(), length());     }     operator std::wstring () const     {         return as_string();     }  private:     jnienv *_env;     jstring _str;     jboolean _is_copy;     const jchar *_pstr; }; 

updated

following code uses string input parameter:

java code:

private static native void log_message(    string category, string message, int level); 

c++ impl:

jniexport void jnicall java_bla_bla_bla_bla_log_1message   (jnienv *env, jclass, jstring category, jstring message, jint level) {     jnicriticalstring pcat(env, category);     if( !pcat.is_valid() )         return;     jnicriticalstring pmsg(env, message);     if( !pmsg.is_valid() )         return;      std::wstring lcat(pcat.c_str(), pcat.length());     std::wstring lmessage(pmsg.c_str(), pmsg.length());     op::logging::instance().log_message(lcat, lmessage, (op::logging::loglevel)level); } 

c++ method return string uses little bit technique:

java_bla_bla_bla_getname(    jnienv *env, jclass operationclass, jlong handler )         {                                                                                                                    std::wstring retval = ...             //.. code resolve std::wstring              return env->newstring(                 (const jchar*)retval.c_str(),                  (jsize)retval.length());           }