JNI and shared library - java-native-interface

Question

Trying to create dll.
So first I created a .java file as follows:
class Main
{
static
{
System.loadLibrary("sample_dll");
}
static native void sritest();
public static void main(String [] a)
{
sritest();
}
}
Then I compile it with no error to .class.
Then using javah I created Main.h.
Then I write following code in c++.
#include <jni.h>
#include <Main.h>
JNIEXPORT void JNICALL Java_Main_sritest(JNIEnv *env,jobject obj)
{
printf("hi");
}
Then I compiled this using MinGw by the following code
g++ -c sample_dll.cpp
g++ -shared -o sample_dll.dll sample_dll.o
Then I place this in java library path.
Then I run Main.java but the following exception occurs
Unstatisfied link error; sritest ()V

Answer 1

I find an answer . It is i do three mistakes. When compiling with c++ we must declare my jni function in extern "C"{} block. Second when compiling in minGW compiler we should use following code and implement include folder of jdk . The code now worked and my program runs smoothly without problem in jni.
The command line code for compiling .o to .dll code is after creating sample_dll.o we must do
g++ -Wall -D_JNI_IMPLEMENTATION -Wl,--kill-at -Ic:/path_of_include_folder_in_jdk_without_drive_letter -Ic:/path_of_win32_folder_in_include_folder_in_jdk_without_drive_letter -shared -o sample_dll.dll sample_dll.o
The last mistake is i want to include Main.h compiled by javah utlity that created from my java code.
This is done by
Javac Main.java
Javah Main
Then take the header file Main.h created and place it in the c++ compiler's include folder. That in my computer c:\minGW\include .
In c++ code add additional preprocessor
#include<Main.h>
All done create dll and place it in one of default java library path . The paths can be getted by using the following function in java
System.out.println (System.getProperty ("java.library.path"));