error: base operand of ‘->’ has non-pointer type ‘JNIEnv’

Question

#include <stdio.h> #include <jni.h>   JNIEnv* create_vm() {     JavaVM* jvm;     JNIEnv* env;     JavaVMInitArgs args;     JavaVMOption options[1];      /* There is a new JNI_VERSION_1_4, but it doesn't add anything for the purposes of our example. */     args.version = JNI_VERSION_1_2;     args.nOptions = 1;     options[0].optionString = "-Djava.class.path=/home/test/workspace/pankajs/"             "jikes/JikesRVMia32-linuxproduction/target/tests/stress/prototype/basic/classes";     args.options = options;     args.ignoreUnrecognized = JNI_FALSE;      JNI_CreateJavaVM(&jvm, (void **)&env, &args);     return env; }  void invoke_class(JNIEnv* env) {     jclass helloWorldClass;     jmethodID mainMethod;     jobjectArray applicationArgs;     jstring applicationArg0;      helloWorldClass = (*env)->FindClass(env, "/test/org/jikesrvm/basic/core/bytecode/TestSwitch");      mainMethod = (*env)->GetStaticMethodID(env, helloWorldClass, "main", "([Ljava/lang/String;)V");      applicationArgs = (*env)->NewObjectArray(env, 1, (*env)->FindClass(env, "java/lang/String"), NULL);     applicationArg0 = (*env)->NewStringUTF(env, "From-C-program");     (*env)->SetObjectArrayElement(env, applicationArgs, 0, applicationArg0);      (*env)->CallStaticVoidMethod(env, helloWorldClass, mainMethod, applicationArgs); }   int main(int argc, char **argv) {     JNIEnv* env = create_vm();     invoke_class( env ); }  I am trying to learn how JVM is actually invoked from bootstrap C files. 

I found this example on internet and I am facing some problems while running it.

I am properly specify the build commands as far as I know as,

  g++ -g -I /usr/lib/jvm/java-6-sun-1.6.0.26/include -I /usr/lib/jvm/java-6-sun-1.6.0.26/include/linux CallJVM.c 

My intention is to actually run it using jikesrvm but to experiment this I chose to work with JVM. The error I am getting is :

CallJVM.c: In function ‘JNIEnv* create_vm()’: CallJVM.c:14:4: warning: deprecated conversion from string constant to ‘char*’ CallJVM.c: In function ‘void invoke_class(JNIEnv*)’: CallJVM.c:28:26: error: base operand of ‘->’ has non-pointer type ‘JNIEnv’ CallJVM.c:30:21: error: base operand of ‘->’ has non-pointer type ‘JNIEnv’ CallJVM.c:32:26: error: base operand of ‘->’ has non-pointer type ‘JNIEnv’ CallJVM.c:32:57: error: base operand of ‘->’ has non-pointer type ‘JNIEnv’ CallJVM.c:33:26: error: base operand of ‘->’ has non-pointer type ‘JNIEnv’ CallJVM.c:34:8: error: base operand of ‘->’ has non-pointer type ‘JNIEnv’ CallJVM.c:36:8: error: base operand of ‘->’ has non-pointer type ‘JNIEnv’ 

I noticed the different ways of implementing in C and C++ but I think I am writing it correctly.

Edit: On compiling with gcc ,I am getting

undefined reference to `JNI_CreateJavaVM' 

and it is what was being prompted in eclipse but I thought my configurations are not apt.When I use ctrl+click it takes me to referenced jni.h as well but still why it is missing reference ? am specifically mentioning my folders on include path.

Answer 1

I noticed the different ways of implementing in C and C++ but I think I am writing it correctly.

You are using the C variant, but are compiling with g++, which invokes the C++ compiler (even if your source file has a .c extension).

Either change the C variants like

(*env)->FindClass(env, ...) 

to the C++ variants, like

env->FindClass(...) 

or switch your compiler to gcc to compile the source as C code.