Calling an external C function from a C file in JNI

Question

Hello,
I am trying to call an external C function, from a C file which is being called by a Java file. I am getting an unresolved symbol error. I have tried many things like, making the external C function in the format of JNI, etc, etc. It is still not working. I think it has something to do with linking the two C files. If anyone can please answer this, it would greatly help me. here is the code:
HelloWorld.c:
#include <jni.h>
#include <stdio.h>
#include "MyOldHello.h"
#include "HelloWorld.h"
JNIEXPORT void JNICALL
Java_HelloWorld_print(JNIEnv *env, jobject obj)
     helloPrint();
     return;
HelloWorld.java:
class HelloWorld
     private native void print();
     public static void main(String[] args)
          new HelloWorld().print();
     static
          System.loadLibrary("HelloWorld");
          System.loadLibrary("MyOldHello");
MyOldHello.c:
#include <jni.h>
#include <stdio.h>
#include "MyOldHello.h"
void helloPrint()
     printf("\nHello World!\n");
MyOldHello.h:
void helloPrint();
Now i use the Visual C++ command prompt to compile this by saying:
javac HelloWorld.java
javah -jni HelloWorld
cl -Ic:\Java\jdk1.6.0_20\include -Ic:\Java\jdk1.6.0_20\include\win32 -MD -LD HelloWorld.c -FeHelloWorld.dll
and now it gives me the error saying that there is an unresolved external symbol, which is the call to helloPrint in the file HelloWorld.
If anyone knows how to solve this, or how to call external C functions from a C file that is being called from a Java file using JNI, please respond.
Thanks
Nick

Answer 1

Hi,
In your post on velocity review, you did not compile MyOldHello.c. You compiled a C file that included the header file for it and called a method defined in the header. The linker is never going to be able to find the code for this if you do not include the object file for this.
Try this. You will also have to add in any JNI libraries you need to link against but I am sure you could work that out.
cl /c MyOldHello.c
cl /c -Ic:\Java\jdk1.6.0_20\include -Ic:\Java\jdk1.6.0_20\include\win32 -MD HelloWorld.c
cl /LD MyOldHello.obj HelloWorld.obj /FeHelloWorld.dll
[http://msdn.microsoft.com/en-us/library/f35ctcxw(VS.80).aspx]
Cheers,
Shane