Android ICS 4.0 NDK NewStringUTF is crashing down

Question

I have a method in JNI C/C++ which takes jstring and returns back jstring some thing like as below,

  NATIVE_CALL(jstring, method)(JNIEnv * env, jobject obj, jstring filename)
  {

// Get jstring into C string format.
  const char* cs = env->GetStringUTFChars (filename, NULL);
  char *file_path = new char [strlen (cs) + 1]; // +1 for null terminator
  sprintf (file_path, "%s", cs);
  env->ReleaseStringUTFChars (filename, cs);


  reason_code = INTERNAL_FAILURE;
  char* info = start_module(file_path);  


  jstring jinfo ;


  if(info==NULL)
  {
      jinfo = env->NewStringUTF(NULL);
  }
  else
  {
      jinfo = env->NewStringUTF(info);

  }


  delete info;

  info = NULL;
  return jinfo;
  }

The code works perfectly with prior android 4.0 versions like 2.2,2.3 and so on. With ICS 4.0 check JNI is on by default and because of it the app crashes throwing the following error

 08-25 22:16:35.480: W/dalvikvm(24027): **JNI WARNING: input is not valid Modified UTF-8: illegal  continuation byte 0x40**
08-25 22:16:35.480: W/dalvikvm(24027):              
08-25 22:16:35.480: W/dalvikvm(24027): ==========
08-25 22:16:35.480: W/dalvikvm(24027): /tmp/create
08-25 22:16:35.480: W/dalvikvm(24027): ==========
08-25 22:16:35.480: W/dalvikvm(24027): databytes,indoorgames,drop
08-25 22:16:35.480: W/dalvikvm(24027): ==========���c_ag����ϋ@�ډ@�����@'
 08-25 22:16:35.480: W/dalvikvm(24027):              in Lincom/inter       /ndk/comNDK;.rootNDK:(Ljava/lang/String;)Ljava/lang/String; **(NewStringUTF)**
08-25 22:16:35.480: I/dalvikvm(24027): "main" prio=5 tid=1 NATIVE
08-25 22:16:35.480: I/dalvikvm(24027):   | group="main" sCount=0 dsCount=0 obj=0x40a4b460   self=0x1be1850
08-25 22:16:35.480: I/dalvikvm(24027):   | sysTid=24027 nice=0 sched=0/0 cgrp=default handle=1074255080
08-25 22:16:35.490: I/dalvikvm(24027):   | schedstat=( 49658000 26700000 48 ) utm=1 stm=3 core=1
08-25 22:16:35.490: I/dalvikvm(24027):   at comrootNDK(Native Method)

I am clueless as to where i am wrong. If you see above NewStringUTF is adding some garbage value to the c Char* bytes .

1. Any idea about why this is happening
2. Any alternative solution to achieve the above is welcome

I really appreciate if one of you can help me in . Thanks in advance

regds me

Answer 1

This works for me in c++

extern "C" JNIEXPORT
jstring Java_com_example_ndktest_MainActivity_TalkToJNI(JNIEnv* env, jobject javaThis, jstring strFromJava)
{
    jboolean isCopy;
    const char* szHTML = env->GetStringUTFChars(strFromJava, &isCopy);

    std::string strMine;
    strMine = szHTML;
    strMine += " --- Hello from the JNI!!";

    env->ReleaseStringUTFChars(strFromJava, szHTML);
    return env->NewStringUTF(strMine.c_str());
}

Answer 2

I had this problem when I change the file Application.mk

From this line:

APP_STL := stlport_static

To:

APP_STL := gnustl_static

Once I changed it back again it fixed the issue.

Answer 3

I also struggled with the same problem from the last day. Finally figured out a solution after a day .. I hope this reply may save someone's day..

The problem was I was calling another function within the native function, used the returned string directly and which caused crash in android older versions

So firstly I saved the string returned from another function to a variable then used it, and the problem gone :D

The below example may clear your concept

//older code with error
//here key_ is the string from java code

const char *key = env->GetStringUTFChars(key_, 0);
const char *keyx = getkey(key).c_str();
return env->NewStringUTF(keyx);

And here is how I solved this error

//newer code which is working
//here key_ is the string from java code

const char *key = env->GetStringUTFChars(key_, 0);
string k = getkey(key);
const char *keyx = k.c_str();
return env->NewStringUTF(keyx);

Happy coding :D

Answer 4

This is how I done this.

1- Char Array to JByteArray.

2- JByteArray to JString.

3- Return jstring to java side.

JNI Code; (.c) format

jstring Java_com_x_y_z_methodName(JNIEnv *env, jobject thiz) {
    int size = 16;
    char r[] = {'P', 'K', 'd', 'h', 't', 'X', 'M', 'm', 'r', '1', '8', 'n', '2', 'L', '9', 'K'};
    jbyteArray array = (*env)->NewByteArray(env, size);
    (*env)->SetByteArrayRegion(env, array, 0, size, r);
    jstring strEncode = (*env)->NewStringUTF(env, "UTF-8");
    jclass cls = (*env)->FindClass(env, "java/lang/String");
    jmethodID ctor = (*env)->GetMethodID(env, cls, "<init>", "([BLjava/lang/String;)V");
    jstring object = (jstring) (*env)->NewObject(env, cls, ctor, array, strEncode);

    return object;
}

Java Code;

native String methodName();

Other Approach Not Works For Me;

I also tried return (*env)->NewStringUTF(env, r) but returns some characters that are not in the char array, at the end of the string where with the warning of JNI WARNING: input is not valid Modified UTF-8: illegal continuation byte 0x40.

Example; PKdhtXMmr18n2L9K�ؾ�����-DL

Edit:

C++ version

jstring clientStringFromStdString(JNIEnv *env,const std::string &str){
//    return env->NewStringUTF(str.c_str());
    jbyteArray array = env->NewByteArray(str.size());
    env->SetByteArrayRegion(array, 0, str.size(), (const jbyte*)str.c_str());
    jstring strEncode = env->NewStringUTF("UTF-8");
    jclass cls = env->FindClass("java/lang/String");
    jmethodID ctor = env->GetMethodID(cls, "<init>", "([BLjava/lang/String;)V");
    jstring object = (jstring) env->NewObject(cls, ctor, array, strEncode);
    return object;
}