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javaandroidc++cjava-native-interface

Calling the Main in c by jni in android


I want to call main:

int main(int argc, char *argv[])

I tried this link: How to use JNI to call a "main" function that takes an array of character pointers?

JNIEXPORT jint JNICALL Java_package_Class_lameMain(JNIEnv *env, jclass class,  jobjectArray jargv)
{    //jargv is a Java array of Java strings
     int argc = env->GetArrayLength(jargv);
     typedef char *pchar;
     pchar *argv = new pchar[argc];
     int i;
     for(i=0; i<argc; i++)
     {
         jstring js = env->GetObjectArrayElement(jargv, i); //A Java string
         const char *pjc = env->GetStringUTFChars(js); //A pointer to a Java-managed char buffer
         size_t jslen = strlen(pjc);
         argv[i] = new char[jslen+1]; //Extra char for the terminating null
         strcpy(argv[i], pjc); //Copy to *our* buffer. We could omit that, but IMHO this is cleaner. Also, const correctness.
         env->ReleaseStringUTFChars(js, pjc);
     }

     //Call main
     main(argc, argv);

    //Now free the array
    for(i=0;i<argc;i++)
       delete [] argv[i];
   delete [] argv;   
 }   

but it doesn't work because I'm programming on C not C++. after I make some changes there is a problem in "GetArrayLength" this error:

error: request for member 'GetArrayLength' in something not a structure or union

I also tried this link: How to call the main function in C file by JNI in Android?

 JNIEXPORT return_type JNICALL Java_full_package_name_classname_functionname(JNIEnv *env, jobject object, Jobject stringArray){
// your argc
int size = env->GetArrayLength(stringArray);
char **argv = new char*[size];
for (int i=0; i < size; ++i) 
{
    jstring string = env->GetObjectArrayElement(stringArrays, i);
    const char* cString = env->GetStringUTFChars(string, 0);
    argv[i] = strdup(cString);
    env->ReleaseStringUTFChars(string, myarray);
    env->DeleteLocalRef(string);
}
// you will need to modify main so it does properly cleanup
main(argc, argv);
// clean up
for(int i = 0; i < size; ++i)
    free(argv[i]);
delete [] argv;
}

the error was: expected ';' or ',' befor Java_package_Class_lameMain


Solution

  • Do like this with repdect to your functions:

    JNIEXPORT void JNICALL Java_ClassName_MethodName
      (JNIEnv *env, jobject obj, jstring javaString)
    {
    
        const char *nativeString = (*env)->GetStringUTFChars(env, javaString, 0);
    
        (*env)->ReleaseStringUTFChars(env, javaString, nativeString);
    }
    

    The thing is to use *env

    See C-example here http://en.wikipedia.org/wiki/Java_Native_Interface