How to pass value of char string to java string (JNI to Java) in function parameter?

Question

Hi I want to pass a character string to java from jni to java in android-ndk. suppose this is my native function.

private native int myFunc(String buffer);

This is my native function in jni:

jint Java_com_example_twolibs_myFunc(JNIEnv*  env, jobject  thiz, jstring buffString){
    //I want to pass a character array to buffString from here, that I would read from java as String.
return 0;
}

How to do it?

I don't think you can do this - reassign a new value to the object passed as parameter. I would create the new string object and return it. — Violet Giraffe
– Violet Giraffe, Commented Sep 21, 2012 at 11:16

fadden · Accepted Answer · 2011-04-19 21:08:35Z

2

I can't quite parse the question. Passing a String "to java from jni to java" sounds redundant.

If all you want is to get at the contents of the String from native code, you can use the JNI GetStringUTFChars to get a UTF-8 representation. Strings are immutable and can't be modified directly. You can create a new String from native with NewStringUTF.

Note that the string data passed to NewStringUTF must be in "modified UTF-8" form. See the JNI docs for an explanation of what that means.

If all you want to do is pass characters around, you may want to use a char[] buffer instead (GetCharArrayElements, ReleaseCharArrayElements). Note that Java language characters are UTF-16, so "jchar" is an unsigned 16-bit value (don't try to treat them as C++ 8-bit "char").

answered Apr 19, 2011 at 21:08

fadden

52.5k5 gold badges119 silver badges173 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

StarDust Over a year ago

I want to call the result = myFunc(testString) where testString will contain value passed from the jni. Note: I'm creating the testString in the Java and passing to the native function. GetStringUTFChars is used to get the value from jstring, but how to set the value to jstring buffer in the native function?

fadden Over a year ago

Java-language Strings are immutable. You can't rewrite them from JNI. You can use NewStringUTF to create a new string, and then return it from your JNI method (which will need to return jstring rather than jint).

Amit Hooda · Accepted Answer · 2012-10-17 10:03:11Z

1

Take a look at this , Tells you how to pass values to ndk and how to retrieve values and performing operation within ndk

http://hoodaandroid.blogspot.in/2012/07/working-with-android-ndk-native.html

answered Oct 17, 2012 at 10:03

Amit Hooda

2,1443 gold badges24 silver badges40 bronze badges

Collectives™ on Stack Overflow

How to pass value of char string to java string (JNI to Java) in function parameter?

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related