An Introduction to JNI using a Bottom Up Approach: Step 3

Continued from An Introduction to JNI using a Bottom Up Approach: Step 2. Note: These steps may be followed without the first step below, if you remove the two references to CPPHelper in the C code and remove "CPPHelper.cpp" from the commands to compile and run "CToCPPHelper.exe".

Step 3: C Main Function

1. Comment out the main function in "CPPHelper.cpp".
   /*  Uncomment to compile and run CPPHelper.exe  
   int main()
   {
    cout << "CPP_HELPER MAIN START" << endl;
    cppHelperEntryPoint();
    cout << "CPP_HELPER MAIN FINISH" << endl;
   }
   */
2. In your working directory, add an empty file, named "CToCPPHelper.h"
3. In your working directory, add the following code, in a file named "CToCPPHelper.cpp":
   #include "CToCPPHelper.h"
   #include "CPPHelper.h" // Comment to ignore CPPHelper
   #include <jni.h>
   #include <stdio.h>
   
   void cToCPPHelperExitPoint() {
       printf("C_TO_CPP_HELPER EXIT START\n");
       cppHelperEntryPoint(); // Comment to ignore CPPHelper
       printf("C_TO_CPP_HELPER EXIT FINISH\n");
   }
   
   int main()
   {
       printf("C_TO_CPP_HELPER MAIN START\n");
       cToCPPHelperExitPoint();
       printf("C_TO_CPP_HELPER MAIN FINISH\n");
   }
   
   JNIEXPORT void JNICALL Java_com_mycompany_myapp_JavaToCHelper_cToCPPHelperEntryPoint(JNIEnv *env, jobject thisObj)
   {
       printf("C_TO_CPP_HELPER ENTRY START\n");
       cToCPPHelperExitPoint(); // Comment to ignore CPPEntryPoint
       printf("C_TO_CPP_HELPER ENTRY FINISH\n");
   }
4. Compile the code and run "CToCPPHelper.exe", using the following commands:
   cd /D "C:\Users\Scott\workspace\myrepo\my-app\src\main\resources\dlls"
   
   "C:\MinGW64\bin\g++.exe" -I"C:\Program Files\Java\jdk1.6.0_26\include" -I"C:\Program Files\Java\jdk1.6.0_26\include\win32" -o CToCPPHelper.exe CToCPPHelper.c CPPHelper.cpp PrintOpenWindows.cpp
   
   CToCPPHelper.exe

   Code Formatted by ToGoTutor

Continued at An Introduction to JNI using a Bottom Up Approach: Step 4.

This post was reposted from http://scottizu.wordpress.com/2013/08/21/an-introduction-to-jni-using-a-bottom-up-approach-step-3/, originally written on August 21st, 2013.