Data through JNI is not passing properly

Question

I am using JNI to call the native C++ layer.

java layer

int res= recog(audioFilePath, grammarFilePath, contextID, subContextID);

C++ layer

JNIEXPORT void JNICALL Java_com_uniphore_voice_recogniser_NuanceOfflineRecogniser_recog(JNIEnv *jenv, jobject jobj, jstring jaudioFilePath, 
                           jstring jgrammarFilePath, <br/>
                           jstring jcontextID, 
                           jstring jsubContext)
{

const char* _audioFilePath      = (char*)jenv->GetStringChars(jaudioFilePath, JNI_FALSE);
const char* _grammarFilePath    = (char*)jenv->GetStringChars(jgrammarFilePath, JNI_FALSE);
const char* _contextId          = (char*)jenv->GetStringChars(jcontextID, JNI_FALSE);
const char* _subContextId       = (char*)jenv->GetStringChars(jsubContext, JNI_FALSE);

std::wcout  << "audio file path: "  << _audioFilePath   <<" "<< std::strlen(_audioFilePath) <<std::endl
            << "grammar file path: "<< _grammarFilePath <<" "<<std::strlen(_grammarFilePath) << std::endl
            << "contextId: "        << _contextId       << std::endl
            << "subContextId: "     << _subContextId    << std::endl << std::endl;

I can see at java layer values is properly passed to the lower level but in c++ layer while printing that value in C++ layer I can see it is printing only first character of whole string.

suppose if audioFilePath I am passing like "c:\\test.wav" I am getting print in c++ layer only like c

I am trying in visual studio 2013 and project character support I selected as Unicode support.

I am new to c++ environment, please help to get the reason for this one.

Answer 1

According to JNI docs GetStringChars returns the unicode characters for the given string in a jchar * which is an unsigned short * . You cast it to a char * . When you use cout with a char * it expects a string in ASCII format with a null-terminator. You pass it a pointer to a string in unicode format, which has every other character 0 for plain ASCII characters. Hence why you only print the first character in the string.

Answer 2

GetStringChars is not returning a pointer to single byte characters, but two byte, unicode characters

const jchar * GetStringChars(JNIEnv *env, jstring string,
jboolean *isCopy);

Returns a pointer to the array of Unicode characters of the string.

Instead, try

GetStringUTFChars

This will be null terminated also.