Invoke Java from C++

I am trying to invoke the Java Virtual machine from C++ following the example found here:

Basically I have a small Java program:

public class TestJNIInvoke
{
    public static void main(String[] args)
    {
    System.out.println(args[0]);
    }
}

Then I have a C++ program that I want to create a JVM and call the TestJNIInvoke class:

#include <jni.h>
#include <cstdlib>
#define PATH_SEPARATOR ';' /* define it to be ':' on Solaris */
#define USER_CLASSPATH "." /* where Prog.class is */

using namespace std;

int main() {
     JNIEnv *env;
     JavaVM *jvm;
     jint res;
     jclass cls;
     jmethodID mid;
     jstring jstr;
     jclass stringClass;
     jobjectArray args;

 #ifdef JNI_VERSION_1_2
     JavaVMInitArgs vm_args;
     JavaVMOption options[1];
     options[0].optionString =
         "-Djava.class.path=" USER_CLASSPATH;
     vm_args.version = 0x00010002;
     vm_args.options = options;
     vm_args.nOptions = 1;
     vm_args.ignoreUnrecognized = JNI_TRUE;
     /* Create the Java VM */
     res = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);
 #else
     JDK1_1InitArgs vm_args;
     char classpath开发者_StackOverflow中文版[1024];
     vm_args.version = 0x00010001;
     JNI_GetDefaultJavaVMInitArgs(&vm_args);
     /* Append USER_CLASSPATH to the default system class path */
     sprintf(classpath, "%s%c%s",
             vm_args.classpath, PATH_SEPARATOR, USER_CLASSPATH);
     vm_args.classpath = classpath;
     /* Create the Java VM */
     res = JNI_CreateJavaVM(&jvm, &env, &vm_args);
 #endif /* JNI_VERSION_1_2 */

     if (res < 0) {
         fprintf(stderr, "Can't create Java VM\n");
         exit(1);
     }
     cls = (*env)->FindClass(env, "TestJNIInvoke");
     if (cls == NULL) {
         goto destroy;
     }

     mid = (*env)->GetStaticMethodID(env, cls, "main",
                                     "([Ljava/lang/String;)V");
     if (mid == NULL) {
         goto destroy;
     }
     jstr = (*env)->NewStringUTF(env, " from CPP!");
     if (jstr == NULL) {
         goto destroy;
     }
     stringClass = (*env)->FindClass(env, "java/lang/String");
     args = (*env)->NewObjectArray(env, 1, stringClass, jstr);
     if (args == NULL) {
         goto destroy;
     }
     (*env)->CallStaticVoidMethod(env, cls, mid, args);

 destroy:
     if ((*env)->ExceptionOccurred(env)) {
         (*env)->ExceptionDescribe(env);
     }
     (*jvm)->DestroyJavaVM(jvm);
 }

But When I try to compile the C++ program I get this error:

c:\java\JNI> g++ -I"c:\Program Files\Java\jdk1.7.0\include"-I"c:\ProgramFiles\Java\jdk1.7.0\include\win32" -c TestJNIInvoke.cpp


TestJNIInvoke.cpp: In function 'int main()':
TestJNIInvoke.cpp:20:31: warning: deprecated conversion from string constant to
'char*'
TestJNIInvoke.cpp:44:18: error: base operand of '->' has non-pointer type 'JNIEn
v'
TestJNIInvoke.cpp:49:18: error: base operand of '->' has non-pointer type 'JNIEn
v'
TestJNIInvoke.cpp:54:19: error: base operand of '->' has non-pointer type 'JNIEn
v'
TestJNIInvoke.cpp:58:26: error: base operand of '->' has non-pointer type 'JNIEn
v'
TestJNIInvoke.cpp:59:19: error: base operand of '->' has non-pointer type 'JNIEn
v'
TestJNIInvoke.cpp:63:12: error: base operand of '->' has non-pointer type 'JNIEn
v'
TestJNIInvoke.cpp:66:16: error: base operand of '->' has non-pointer type 'JNIEn
v'
TestJNIInvoke.cpp:67:16: error: base operand of '->' has non-pointer type 'JNIEn
v'
TestJNIInvoke.cpp:69:12: error: base operand of '->' has non-pointer type 'JavaVM'

Any ideas?

Thanks

Even though you include the same header file, the Java Native Interface uses two different interfaces for C and C++.

In C++, it's:

jclass cls = env->FindClass("java/lang/String");

instead of (for C):

jclass cls = (*env)->FindClass(env, "java/lang/String");

So the C function call that requires env in two places becomes a convenient member function call in C++.

This is mentioned in the Native Method Arguments section of the Java Native Interface 6.0 Specification.

My guess would be that you're attempting to compile against the win32 headers given the command line you're using. Have you tried -I"c:\ProgramFiles\Java\jdk1.7.0\include\solaris instead (assuming that's your platform based on the comment higher up in the source).