Using JNI from Managed C++

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dorkrawk@gmail.com - 27 Jul 2006 19:13 GMT

Hey, I'm working with a Java Native Interface from managed C++
(MS Visual C++ .net 2003... if these details help) and I keep having
issues with mixing managed and nonmanaged types for example...

[code]
__value __nogc struct JNI_Interface
{
    JavaVM __nogc *jvm; /* denotes a Java VM */
    JNIEnv __nogc *env; /* pointer to native method interface */
    //static jobject phone_obj; // phone object to make JNI calls to PTF
with

    int jni_startJVM();
    int jni_checkException(char* jni_call);
    int jni_startCom();
};
[/code]
[code]
JNI_Interface::jni_startJVM()
{
...
jint res = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args); // error on
this line
...
}
[/code]

causes this error (error thrown on JNI_CreateJavaVM() call)....

jni.cpp(34) : error C2440: 'type cast' : cannot convert from 'JNIEnv
*__gc * ' to 'void ** '
Cannot convert a managed type to an unmanaged type
jni.cpp(34) : error C2664: 'JNI_CreateJavaVM' : cannot convert
parameter 1 from 'JavaVM *__gc * ' to 'JavaVM ** '
Cannot convert a managed type to an unmanaged type

I've tried all sorts of __nogc stuff but it keeps throwing these errors
on build. Does anybody have any ideas or has anyone else worked w/ JNI
within managed C++?

Reply to this Message

Chris Uppal - 28 Jul 2006 09:29 GMT

> Hey, I'm working with a Java Native Interface from managed C++

Boy! You're no fan of the simple life are you ?

;-)

I haven't done /anything/ with "managed C++", so take the rest of this with due
caution.

For a start, I wouldn't mess with the declarations the SUN provide -- they are
carefully designed to allow the JVM to access stuff at a lower level than
"portable C" (or C++). I.e. it knows about memory layouts and other such
stuff. So what I would do, as a first attempt, would be to write a bridge
component -- entirely in /real/ C++ (compiled to a normal, not .NET, DLL).
That component would do all the talking to JNI. I would then create a .NET
interface to that DLL, using the unmanaged C++ features.

A lot of work, and maybe not necessary, but I'd be rather surprised to find
that anything less complicated actually worked.

However, even that might not work. There is no guarantee that the Sun JVM and
the .NET equivalent will be happy sharing an address space. They both use very
low-level features of the OS (like setting guard pages, directly accessing the
processor stack, and so on) and might easily end up stepping on each other's
feet.

-- chris

Reply to this Message

Vitaly - 30 Jul 2006 15:15 GMT

Hi,
see JNI SDK for .NET at
http://www.simtel.net/product.php[id]95126[sekid]0[SiteID]simtel.net
It has the same functionality as Regular JNI for C++.

> Hey, I'm working with a Java Native Interface from managed C++
> (MS Visual C++ .net 2003... if these details help) and I keep having
[quoted text clipped - 35 lines]
> on build. Does anybody have any ideas or has anyone else worked w/ JNI
> within managed C++?

Reply to this Message

Using JNI from Managed C++

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