compiling c file that uses jni.h

Question

I am having trouble compiling the following program

PPConverter.java:

 public class PPConverter {
    private native void convert(String s);
    public static void main(String[] args){
        new PPConverter().convert(args[0]);
    }
    static {
        System.loadLibrary("converter");
    }
}

converter.c:

 #include <jni.h>
 #include <stdio.h>
 #include "PPConverter.h"

 JNIEXPORT void JNICALL Java_PPConverter_convert (JNIEnv *, jobject, jstring){
    printf(jstring);
    return;
  }

Since I am working on UNIX, I am using the following command to compile the converter.c file:

cc -I/usr/lib/jvm/java-6-openjdk/include  converter.c -o libconverter.so

but I am getting the following errors:

converter.c: In function âJava_PPConverter_convertâ:
converter.c:5: error: parameter name omitted
converter.c:5: error: parameter name omitted
converter.c:5: error: parameter name omitted
converter.c:6: error: expected expression before âjstringâ

What am I doing wrong??

Answer 1

In case anyone runs into this error, the problem is that the header file created by javah doesn't specify the name of its parameters (it's just a header file not an implementation). But in your implementation, if you just copy/paste the header file without adding the parameter names you'll get the error.

So the code from your header file (the file generated by javah, don't change this file):

JNIEXPORT void JNICALL Java_PPConverter_convert (JNIEnv *, jobject, jstring);

When you copy it (into your file ending in .c or .cpp), needs to have variable names:

JNIEXPORT void JNICALL Java_PPConverter_convert (JNIEnv *env, jobject obj, jstring mystring){

This will fix it.