Getting Error with the C++ code

Question

I have a function in C++ which accepts a "jstring". And if i write the below line of code it gives me error.
jsprData -> is the jstring INPUT
char sprData = (env)->GetStringUTFChars(env, jsprData, 0);
But the same thing if i write in a "C Code" and build a DLL then it is working fine.
Why so ? Is there any different way to write a code to convert "jstring" to "char *" in C++ ?
Please do reply me.
Thanks in advance.
Patro

Answer 1

When you are using JNI from inside C++ use the wrappers such as JNIEnv, JavaVM instead of the C style calls. I wrote win32 dlls using the invocation API from C++ code and everything gets compiled without a hitch.
Here is a code example method that returns Java exceptions as CString objects:
CYourClassName::GetJavaException(jthrowable exObject)
    CString csExMessage;
    if ( exObject != NULL )
        mp_Env->ExceptionDescribe();
        jclass cls = mp_Env->FindClass ("java/lang/Throwable"); // check for cls to be NULL
        jmethodID method = mp_Env->GetMethodID ( cls,"toString", "()Ljava/lang/String;");
        jstring exMsg = (jstring) mp_Env->CallObjectMethod ( exObject, method ); // Check for NULL
        const char* ps = mp_Env->GetStringUTFChars ( exMsg, NULL);
        csExMessage.Format( "%s\n", ps );
        mp_Env->ReleaseStringUTFChars ( exMsg, ps );
    return csExMessage;
And in your .h file declare a member variable as:
    JNIEnv* mp_Env;
Also, do not forget to initialize mp_Env properly at the beginning. You could use something like this:
    jint ret = JNI_CreateJavaVM(&mp_Jvm, (void **)&mp_Env, &vm_args);
This code compiles and runs.
Hope this helps.
-- Avijit