CODEWITHSUNDEEP
javacjava-native-interface
ARao
ARao

Reputation: 259

Call Java from C using JNI

I'm trying the following code to call a Java function performSHA() from C code. But I keep getting an error saying "request for member ‘DestroyJavaVM’ in something not a structure or union". I've checked several links online and seems like I'm using it as mentioned. 

JavaVM *jvm;       
JNIEnv *env;      
JavaVMOption options[3];
JavaVMInitArgs vm_args; 
vm_args.version  = JNI_VERSION_1_2;

JNI_GetDefaultJavaVMInitArgs(&vm_args);
options[0].optionString = "/home/amy/jni/";
vm_args.options  = options;

JNI_CreateJavaVM(&jvm, &env, &vm_args);
jclass cls = (*env)->FindClass(env, "CallToBCLib");
jmethodID mid = (*env)->GetStaticMethodID(env, cls, "performSHA", "ILjava/lang/String;");
(*env)->CallStaticVoidMethod(cls, mid, algo_id, tc->m1);
jvm->DestroyJavaVM();   <-- ERROR

Also is the usage of FindClass, GetStaticMethodID and CallStaticVoidMethod correct? performSHA is the Java function I'm calling and algo_id, tc->m1 are my args to the Java function...

Upvotes: 0

Views: 518

Answers (3)

ARao
ARao

Reputation: 259

I solved this by doing the following:

(*jvm)->DestroyJavaVM(jvm);

Upvotes: 2

Daniel
Daniel

Reputation: 651

This is a bit too long to be in a comment so I'll put it as an answer. I checked how you should access DestroyJavaVM in the jni source code:
The function is defined here and this is the declaration: 

jint JNICALL jni_DestroyJavaVM(JavaVM *vm)

At the bottom of that page is a function invocation table for usage in C source code.

The specification gives us the definition of the JavaVM type here.
We can see that the definition of the JavaVM type is the function invocation table itself.

This means we need to take our jvm variable and access its DestroyJavaVM function,
while also passing the jvm instance itself, so the accessing code should look like this: 

jvm->DestroyJavaVM(jvm);

I haven't tested this and it's a bit weird to call the function like that but I'm guessing this should work.

Upvotes: 0

syntagma
syntagma

Reputation: 24294

According to the documentation, you should provide a parameter of type JavaVM *vm to the DestroyJavaVM function:

jint DestroyJavaVM(JavaVM *vm);

Therefore, replace jvm->DestroyJavaVM() with DestroyJavaVM(jvm).

Note that on the same page, there is an "Overview" with example where DestroyJavaVM() is called as in your code (jvm->DestroyJavaVM()) but this applies to C++ and you mentioned you are trying to call Java code from C.

Upvotes: 0

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