How to create Java String array with GCJ?

Question

I am trying to call the "public static void main(String[])" method of Java class kissdb.dev.Run from C++ code. I use GCJ to compile:

c++ -c run.cpp; gcj run.o kissdb.so -lstdc++ -o run.x

But code below does not compile. Compiler says:

run.cpp: In function ‘int main(int, char**)’:
run.cpp:52:23: error: no match for ‘operator=’ in ‘*(args + ((unsigned int)(((unsigned int)i) * 8u))) = arg’

What to do? My C++ code:

#include <gcj/cni.h>
#include <java/lang/System.h>
#include <java/io/PrintStream.h>
#include <java/lang/Throwable.h>

#include <iostream>
#include "pub.h"

java::lang::String* js(const char* s) {
    return JvNewStringLatin1(s);
}

int main(int argc, char *argv[]) {   
    using namespace std;                // For cout <<
    using namespace java::lang;         // For System::class, Throwable

    try {
        JvCreateJavaVM(NULL);
        JvAttachCurrentThread(NULL, NULL);

        cout << "* Hello from GCJ! argc: " << argc << endl;

        JArray<String *> *args = 
            (JArray<String *> *) JvNewObjectArray(argc, &String::class$, NULL);
                // From http://gcc.gnu.org/onlinedocs/gcj/Arrays.html#Arrays

        for (int i = 0; i < argc; i++) {
            String* arg = JvNewStringLatin1(argv[i]);
            args[i] = arg;               // <---  ERROR HERE
        }

        kissdb::dev::Run::main(args);    // The Java main method I want to run.

        JvDetachCurrentThread();
    } catch (Throwable *t) {
         System::out->println(js("Unhandled Java exception:"));
         t->printStackTrace();
    }
}

Tom Tromey · Accepted Answer · 2013-06-04 13:31:46Z

2

You need to use the 'elements' template function.

elements(args)[i] = arg;

See the "Arrays" page in the manual.

answered Jun 4, 2013 at 13:31

Tom Tromey

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3 Comments

Frans Lundberg Over a year ago

Great, now it works! Thank you so much! I have not used C++ template functions for many years. I saw the manual, but did not really get it.

Frans Lundberg Over a year ago

Now, I might be able to release my database, kissdb.com for use with GCJ too. KissDB is designed to make it simple, fun, and efficient to store software objects.

Frans Lundberg Over a year ago

I had to rename my database to BergDB, bergdb.com. It now works with GCJ - have not release the GCJ version yet, however.

Dippo · Accepted Answer · 2013-05-30 16:36:48Z

0

I am not 100% sure, because i am not sure how GCJ works. But the args array is already taken by Java. I think that if you use a different name for the args array, that it should work.

Edit: Now i read your post (learning GCJ), i see what you are trying todo. So, my answer is not totaly correct.

edited May 30, 2013 at 16:36

answered May 30, 2013 at 14:00

Dippo

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