JNI error

[Jiafan Zhou]

I followed the JNI tutorial and why everytime I use a gcc compiler to generate a dll in windows, I got the following error.

C:\cjsdn\cjsdn\classes>gcc -I"C:\jdk1.5.0_06\include" -I"C:\jdk1.5.0_06\include\win32" -o hello.dll HelloWorldImp.c
In file included from C:/jdk1.5.0_06/include/jni.h:27,
                 from HelloWorldImp.c:1:
C:/jdk1.5.0_06/include/win32/jni_md.h:16: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'jlong'
In file included from HelloWorldImp.c:1:
C:/jdk1.5.0_06/include/jni.h:108: error: expected specifier-qualifier-list before 'jlong'
C:/jdk1.5.0_06/include/jni.h:193: error: expected ')' before '*' token
C:/jdk1.5.0_06/include/jni.h:195: error: expected ';' before 'jclass'
C:/jdk1.5.0_06/include/jni.h:1862: error: expected ')' before '*' token
C:/jdk1.5.0_06/include/jni.h:1863: error: expected ';' before 'void'
C:/jdk1.5.0_06/include/jni.h:1888: error: expected ')' before '*' token
C:/jdk1.5.0_06/include/jni.h:1890: error: expected ';' before 'jint'
C:/jdk1.5.0_06/include/jni.h: In function '__declspec':
C:/jdk1.5.0_06/include/jni.h:1928: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'JNI_GetDefaultJavaVMInitArgs'
C:/jdk1.5.0_06/include/jni.h:1930: error: expected declaration specifiers before '__declspec'
C:/jdk1.5.0_06/include/jni.h:1933: error: expected declaration specifiers before '__declspec'
C:/jdk1.5.0_06/include/jni.h:1937: error: expected declaration specifiers before '__declspec'
C:/jdk1.5.0_06/include/jni.h:1940: error: expected declaration specifiers before '__declspec'
In file included from HelloWorldImp.c:2:
com_nativeutil_HelloWorld.h:15: error: expected declaration specifiers before '__declspec'
HelloWorldImp.c:5: error: expected declaration specifiers before '__declspec'
HelloWorldImp.c:10: error: expected '{' at end of input

Kind regards,
Jiafan

[Jiafan Zhou]

The gcc I am using now is:

gcc.exe (GCC) 4.1.0
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

I wonder if the gcc is compatiable with the JNI interface.

Regards,
Jiafan

[Jiafan Zhou]

I also downloaded the MS cl compiler and still does not work with the following exception.

C:\cjsdn\cjsdn\classes>cl -IC:\jdk1.5.0_06\include -IC:\jdk1.5.0_06\include\win32 -LD HelloWorldImp.c -Fehello.dll
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 14.00.50727.42 for 80x86
Copyright (C) Microsoft Corporation.  All rights reserved.
 
HelloWorldImp.c
C:\jdk1.5.0_06\include\jni.h(21) : fatal error C1083: Cannot open include file: 'stdio.h': No such file or directory

Since in the basic c file I was writing, it definately includes the printf..so a stdio.h is definately used..why it complains about the stdio.h not found..

I love Java more than others.

Regards,
Jiafan

[Dan Bizman]

Try hardcoding the include statement to where the ".h" file is. For example:

#include <D:\blah\blah\stdio.h>

(You may have to do this for other ones as well)

[Jiafan Zhou]

I fixed the stdio.h problem by explicitly add a set

INCLUDE=C:/Program Files/Microsoft Visual Studio 8/VC/include

inthe AUTOEXEC.bat..

but I still have the problem when I link the object file into a dll...

LINK : fatal error LNK1104: cannot open file 'LIBCMT.lib'

Jiafan
[ September 18, 2006: Message edited by: Jiafan Zhou ]

[Jiafan Zhou]

I think I fixed the problem with the CL compiler..well I stll have a fatal problem at last..

Exception in thread "main" java.lang.UnsatisfiedLinkError: displayHelloWorld
at com.nativeutil.HelloWorld.displayHelloWorld(Native Method)
at com.nativeutil.HelloWorld.main(HelloWorld.java:40)

Do I need to setup a LD_LIBRARY_PATH Environment Variable?( I have created one where I located my dll and exp files)

Regards,
Jiafan

[Ernest Friedman-Hill]

LD_LIBRARY_PATH is a Unix thing only.

Use the -Djava.library.path=<path> Java command-line switch.

[Jean-Francois Briere]

1- When using gcc you must add the following compiler/linker flags:

-D__int64="long long"
-shared
-Wl,--add-stdcall-alias

So that your command line should look like:

gcc -D__int64="long long" -I"C:\jdk1.5.0_06\include" -I"C:\jdk1.5.0_06\include\win32" -shared -Wl,--add-stdcall-alias -o hello.dll HelloWorldImp.c

Also if your are using gcc under Cygwin you should also use the flag -mno-cygwin to be able to run your program outside Cygwin.


2- When using MS cl.exe and link.exe you should allways first call vcvars32.bat located in the MSVC bin folder
(C:\Program Files\Microsoft Visual Studio 8\VC\bin for instance).
This script sets all the necessary variables to the appropriate values.
There is albsolutely NO NEED to set anything by hand.
And I wouln't call it in autoexec.bat since this will load your system/user environment at any time,
even when you are not building c/c++ files.


3- When you have successfully build your DLL you should either:
a- Put it in a folder already pointed by the Path enviroment variable (usually not a good idea)
b- Update the Path enviroment variable to add the folder where your DLL is located.
You could do that each time just before executing the Java program:
>set Path=yourDllFolder;%Path%
>java YourClass
You could also update your Path enviroment variable once and for all with the help of the 'System Properties' window.
c- (Preferably) Set the folder of your DLL while executing your Java program with the java.library.path property:
> java -Djava.library.path=yourDllFolder YourClass


Regards

[Jiafan Zhou]

I still have the following error..

C:\cjsdn\cjsdn>java -Djava.library.path=. com.nativeutil.HelloWorld
Exception in thread "main" java.lang.UnsatisfiedLinkError: displayHelloWorld
        at com.nativeutil.HelloWorld.displayHelloWorld(Native Method)
        at com.nativeutil.HelloWorld.main(HelloWorld.java:40)

Regards,
Jiafan

[Jiafan Zhou]

It works...

I made a silly mistake in the C program which does not make the function signature same in the .h file.

I will post the c program in a second for others to track the errors.

#include <jni.h>
#include "com_nativeutil_HelloWorld.h"
#include <stdio.h>
 
JNIEXPORT void JNICALL 
Java_com_nativeutil_HelloWorld_displayHelloWorld(JNIEnv *env, jobject obj) 
{
    printf("Hello world!\n");
    return;
}

Notice that I used the fully qualified package modifier here, I ignored this for the first time and it ends up with errors in the runtime.

Thanks guys very much for the help.
[ September 19, 2006: Message edited by: Jiafan Zhou ]

[Dan Bizman]

Originally posted by Jean-Francois Briere:
1- When using gcc you must add the following compiler/linker flags:

-D__int64="long long"
-shared
-Wl,--add-stdcall-alias

So that your command line should look like:

gcc -D__int64="long long" -I"C:\jdk1.5.0_06\include" -I"C:\jdk1.5.0_06\include\win32" -shared -Wl,--add-stdcall-alias -o hello.dll HelloWorldImp.c

Also if your are using gcc under Cygwin you should also use the flag -mno-cygwin to be able to run your program outside Cygwin.


2- When using MS cl.exe and link.exe you should allways first call vcvars32.bat located in the MSVC bin folder
(C:\Program Files\Microsoft Visual Studio 8\VC\bin for instance).
This script sets all the necessary variables to the appropriate values.
There is albsolutely NO NEED to set anything by hand.
And I wouln't call it in autoexec.bat since this will load your system/user environment at any time,
even when you are not building c/c++ files.


3- When you have successfully build your DLL you should either:
a- Put it in a folder already pointed by the Path enviroment variable (usually not a good idea)
b- Update the Path enviroment variable to add the folder where your DLL is located.
You could do that each time just before executing the Java program:
>set Path=yourDllFolder;%Path%
>java YourClass
You could also update your Path enviroment variable once and for all with the help of the 'System Properties' window.
c- (Preferably) Set the folder of your DLL while executing your Java program with the java.library.path property:
> java -Djava.library.path=yourDllFolder YourClass


Regards

This is an awesome post and I vote for it as one of the best/most informative posts ever.

It raises the question, however, as to why Sun's JNI tutorial doesn't mention any of this.

[Ernest Friedman-Hill]

Originally posted by Dan Bizman:

It raises the question, however, as to why Sun's JNI tutorial doesn't mention any of this.

Because some of it is subjective opinion, and its validity depends on some unstated assumptions about versions of various things. Not saying it's not useful, but for some folks this recipe wouldn't work.

Note that Sun's JNI tutorial ain't there anymore -- I'd guess because providing compiler recipes which worked for everyone was getting too tricky.

[Jiafan Zhou]

I cant agree more.

Jiafan