[Swig-devel] simple question about longs and Java

[Dan N. <Dan.Nietupski@GlobalGeophysical.com>]

Hi,

I have a very simple question and example about the use of longs when interfacing with Java.

SWIG is insisting to change longs to ints. Why and can I get around it?


Here is example.i:

%module example
%{
void tryLong(long);
%}
void tryLong(long);


Here is example.cxx:

#include <stdio.h>

void tryLong(long myLong)
{
    printf("myLong=%ld\n",myLong);
}


Here is a fragment of the automatically generated C++ wrapper code. Notice that SWIG changed the argument to tryLong to jint and then used an intermediate cast to long before calling tryLong with a long.

JNIEXPORT void JNICALL Java_exampleJNI_tryLong(JNIEnv *jenv, jclass jcls, jint jarg1) {
  long arg1 ;

  (void)jenv;
  (void)jcls;
  arg1 = (long)jarg1;
  tryLong(arg1);


Here is the automatically generated example.java:

public class example {
  public static void tryLong(int arg0) {
    exampleJNI.tryLong(arg0);
  }

}

This is causing me trouble because my main code is Java that has longs that I need to send to native code.

Additional Info.

Using swig 2.0.11 on Linux (CentOS release 5.6 (Final)).

This is how I ran the example:

setenv CLASSPATH .
setenv LD_LIBRARY_PATH .
swig -java -c++ example.i
g++ -c example.cxx example_wrap.cxx -fpic -fno-strict-aliasing -I$JDK_HOME/include -I$JDK_HOME/include/linux
g++ -shared example.o example_wrap.o -o libexample.so
javac *.java
java tester

Here is tester.java where I was forced to use an int:

public class tester
{
    public static void main(String argv[])
    {
        System.loadLibrary("example");
        System.out.println("example");
        int myLong = 1;
        example.tryLong(myLong);
    }
}


If I use a long, I get this error:

tester.java:8: tryLong(int) in example cannot be applied to (long)
        example.tryLong(myLong);
               ^
1 error
Exception in thread "main" java.lang.NoClassDefFoundError: tester
Caused by: java.lang.ClassNotFoundException: tester
        at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:247)




Here is the automatically generated exampleJNI.java:

class exampleJNI {
  public final static native void tryLong(int jarg1);
}