JNI: printf displays strange characters

Question

Hi,
i'm tryng to understand how JNI works...
I've writen a simple class in Java and i'm trying to pass a variable to a native method ...
This is my java class
public class Encrypt {
     static {
          System.loadLibrary("endecrypt");
     public native void encRec(byte[] p1);
     private static void encryptFile() {
          String p1 = "12345678";
          new Encrypt().encRec(p1.getBytes());
     public static void main(String[] args) {
          encryptFile();
}This is the native C method
#include <jni.h>
#include <stdio.h>
     JNIEXPORT jint JNICALL Java_Encrypt_encRec(JNIEnv *jenv, jobject jobj, jbyteArray p1) {
          jboolean isCopy = 0;
          unsigned char *pwd1;
          pwd1 = (unsigned char *)(*jenv)->GetByteArrayElements(jenv, p1, &isCopy);
          printf("[log - ENCRYPT]...........");printf("\n");
          printf("[log - pwd1] "); printf(pwd1);printf("\n");
          (*jenv)->ReleaseByteArrayElements(jenv, p1, pwd1, 0);          
          return 0;
     }and this is my bat file
javac Encrypt.java                                                                               
javah -o encrypt_jni.h Encrypt                                                                     
cl -IC:\j2sdk1.4.2_05\include -IC:\j2sdk1.4.2_05\include\win32 -LD Encrypt.c -Feendecrypt.dll    
java Encrypt                                                                                     
pause                                                                                             when i run it the result i get is:
[log - ENCRYPT]...........
[log - pwd1] 12345678@&#9787;&#9787;The question is: What are the strage characters at the end of the password? What am i doing wrong?

Answer 1

Your original byte array just contained the characters "12345678" and
you were just lucky that there was an ASCII NUL (one ell) character
in the vicinity before the entire thing dumped core against you.
Using C, a string is defined as a bunch of ASCII characters terminated
by a NULL (one ell, all bits zero) character. Java uses a different approach:
a byte array knows what its length is. The decision is up to you: supply
a NUL byte to the C stuff for convenience or use the supplied length
from the byte array when you're in the C part of the JNI barrier.
kind regards,
Jos