getting variable of c in java

[preethi Ayyappan]

Hi,

I need to get a variabe which is in a c program through java.Is it possible.if so.please help me with some link.

Thanks

[Campbell Ritchie]

Try googling for JNI which means Java Native Interface, see whether there is anything in that which can help.

[preethi Ayyappan]

Thankyou for your response.i will look at that

[Campbell Ritchie]

You're welcome. I don't know whether it will work, but the JNI is the usual interface between Java and C.

[preethi Ayyappan]

Hi,
I have tried a sample from JNI and tried to get the out put of c through java.I am posting the java and c code:

JNIDemo.java

 
public class JNIDemo 
{ public native void display();
static{System.loadLibrary("Nativecode");
} 
public static void main(String args[]) 
{
try {JNIDemo jdo=new JNIDemo();
jdo.display();
}
catch(Exception e)
{
System.out.println("Alert Alert Alert:"+e.getMessage());
}
}
}

Nativecode.c

  
#include "JNIDemo.h" 
JNIEXPORT void JNICALL Java_JNIDemo_display(JNIEnv *env, jobject obj) 
{
char name[30];
printf("What is your name?\n");
scanf("%s",&name); 
printf("Hello,%s I am from C\n",name);
 }
 int main()
 {
 return 0;
}
  

I compiled the java program and created header file too.Then i have created library like

cc -o libnativecode.so -shared -I/usr/java/jdk/include -I/usr/java/jdk/include/linux Nativecode.c

Now libNativecode.so file is created in the dir /usr/java/jdk/include/linux.
Then I set the path environment variable to point the library file like

export LD_LIBRARY_PATH=/usr/java/jdk/include/linux:$LD_LIBRARY_PATH:

Then i run the java file like java JNIDemo.I am getting the following error:

Exception in thread "main" java.lang.UnsatisfiedLinkError: libNativecode: libNativecode.so: cannot open shared object file: No such file or directory
at java.lang.Runtime._load(libgcj.so.7rh)
at java.lang.Runtime.loadLibrary(libgcj.so.7rh)
at java.lang.System.loadLibrary(libgcj.so.7rh)
at JNIDemo.<clinit>(JNIDemo.java:3)
at java.lang.Class.initializeClass(libgcj.so.7rh)

I think i am wrong in setting the library path.Please point out me where am i wrong and help me to solve this problem.

Thanks in Advance

[subhajit paul]

when you said

    System.loadLibrary("NativeCode");    

the library is looked for in the directories that are included in the PATH variable, commonly /usr/bin or /usr/sbin .

however, it seems you compiled the code like:

cc -o libNativeCode.so ... NativeCode.c

which might have left the library(.so file) in your source code directory(assuming you saved the source file in home directory) itself.

try using

System.Load(AbsolutePathToLibrary)

where AbsolutePathToLibrary is a String like "~/libNativeCode.so" or"./libNativeCode.so"

[Charles Lyons]

You need to tell Java where to find your library. This should work:

java -Djava.library.path=PATH_TO_LIB JNIDemo

where PATH_TO_LIB is the path to the directory containing your library, which may be "." if it's in the current directory.