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Thread: Store a random C buffer inside a Java String

  1. #1
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    Default Store a random C buffer inside a Java String

    Hello,

    due to compatibility reasons, I need to be able to store a random C buffer inside of a Java String. THis means that the Java String should contain the exact same buffer information (i.e. byte sequence) as the original C buffer. How would I do that?

    All the functions I found will always somehow code/decode the C buffer, and modify its content depending on the selected encoding.

    I need to doo this inside JNI. Following is what I have:

    	unsigned char* cBuffer=getCBuffer();
     
    	// Transfer the C buffer to s:
    	jstring s=NULL;
       	if (env->EnsureLocalCapacity(2) >= 0)
    	{
    		jbyteArray bytes = env->NewByteArray(signalLength);
    		if (bytes != NULL) 
    		{
    			env->SetByteArrayRegion(bytes, 0, signalLength,(jbyte *)cBuffer);
    			jclass cls = env->FindClass("java/lang/String");
    			jmethodID mid = env->GetMethodID(cls, "<init>", "([B)V");
    			s = (jstring)env->NewObject(cls, mid, bytes);
    			env->DeleteLocalRef(bytes);
    		}
    	}

    Thanks for any help


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    Default Re: Store a random C buffer inside a Java String

    Welcome to the forum! Thanks for taking the time to learn how to post code correctly. If you haven't already, please read this topic to learn other useful info for new members.

    Requiring something to be or do something it simply cannot be or do is not a reasonable requirement. Instead, modify your requirement to decode/encode so that the buffer is represented appropriately for the situation.

  3. #3
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    Default Re: Store a random C buffer inside a Java String

    due to compatibility reasons, I need to be able to store a random C buffer inside of a Java String. THis means that the Java String should contain the exact same buffer information (i.e. byte sequence) as the original C buffer. How would I do that?
    Unfortunately, I don't know what environment your coding in, Linux, Windows etc. But I'll assume Windows. First of all, strings are different in C and Java. In Java they are sequences of UTF-16 code points whereas C strings are null terminated sequence of bytes. I believe JNI has two the functions for manipulating these strings. One is "modified UTF-8" byte sequences and the other is arrays of UTF-16 values.

    Windows has two types of strings ASCII and Unicode. If your C code is using ASCII strings then use the "modified UTF-8 conversion functions. Otherwise, if you are using Unicode strings then UTF-16 conversion functions are what you need.

    Finally, I can't be of much help to you since my Java experience is minimal. But you do have to convert the strings as indicated above.

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