An example showing how to assign a function table to a C struct in one go

jni_headers_example_2.c

#include <stdio.h>
#include <stdlib.h>

/** jni.h **********************************************************************************/
struct JNINativeInterface_ {
    void *reserved0;
    void *reserved1;
    void *reserved2;
    void *reserved3;
    
    int (*GetVersion)(int* version);
};
/**
 * Construct a memory reference type
 */
typedef struct JNINativeInterface_* JNIEnv;

/**
 * Implementation
 */
int GetVersion(int* version) {
    return 0b10 * (*version);
}

JNIEnv* env = NULL;
/** jni.h **********************************************************************************/

/** jni.c **********************************************************************************/
/**
 * Initializes the JNI interface function table.
 * 
 * @param env a pointer to the JNIEnv address to be allocated.
 */
static inline void init_jni(JNIEnv** env) {
    struct JNINativeInterface_ jni_interface = {
        NULL,
        NULL, 
        NULL, 
        NULL,
        
        &GetVersion
    };
    
    *env = (JNIEnv*) calloc(1, sizeof(char));
    **env = &jni_interface;
}

int main() {
    
    init_jni(&env);
    /** jni.c **********************************************************************************/ 
   
    /** user code**********************************************************************************/
    int java = 8;
    int jni_version = (*env)->GetVersion(&java);
    printf("%i\n", jni_version);
    
    free(env);

    return 0;
}