I am trying to make a proof of concept where in a cpp program I fetch the windows username and then call this program from a java code, using Java native interface(JNI). Now what i have so far is, a sample JNI hello world program which is able to compile and print Hello world or what what ever parameter I set up. Now in a separate cpp snippet i am able to fetch the current username and it works as well; looks as follows:
#include <iostream>
#include <windows.h>
using namespace std;
int main()
{
char acUserName[100];
DWORD nUserName = sizeof(acUserName);
if (GetUserName(acUserName, &nUserName)) {
cout << "User name is " << acUserName << "." << endl;
cin.get();
}
return 0;
}
When compiled and executed using my G++ in command prompt it prints the current username correctly.
Now i just want to combine the two programs. When I do that as follows
public class Sample1
{
public native String fetchCurrentUserName();
public static void main(String[] args)
{
System.loadLibrary("Sample1");
Sample1 sample = new Sample1();
String userName = sample.fetchCurrentUserName();
System.out.println("userName: " + userName);
}
}
This is the java part and the cpp part is as follows:
#include "Sample1.h"
#include <string.h>
#include <iostream>
#include <windows.h>
using namespace std;
JNIEXPORT jstring JNICALL Java_Sample1_fetchCurrentUserName
(JNIEnv *env, jobject obj) {
char acUserName[100];
DWORD nUserName = sizeof(acUserName);
if (GetUserName(acUserName, &nUserName)) {
cout << "User name is " << acUserName << "." << endl;
cin.get();
}
const char* userName = acUserName;
//const char* userName = "acUserName";
return env->NewStringUTF(userName);
}
void main(){}
This does not compile anymore, it says
Sample1.obj : error LNK2019: unresolved external symbol __imp_GetUserNameA referenced in function Java_Sample1_fetchCurrentUserName
Sample1.dll : fatal error LNK1120: 1 unresolved externals
I used the following command to compile the JNI code.
cl -I"C:\Program Files\Java\jdk1.8.0_131\include" -I"C:\Program Files\Java\jdk1.8.0_131\include\win32" -LD Sample1.cpp -FeSample1.dll
as per tutorial from https://www.ibm.com/developerworks/java/tutorials/j-jni/j-jni.html. Now from few other questions in stack overflow it seems somehow my program is unable to link the windows library or leader somehow. But I have no clue as to how this can be solved. Any body have any bright ideas? Please make my day! Thank you for your time :D I looked into Linking of dll file in JNI which is very relevant for my question. But not sure if the solutions are applicable to me.
Edit
error: LNK1120: 5 unresolved externals This question had similar problem and it seems to have same solution which is as suggested by Remy to link with Advapi32.lib. At least now i learned few new things like #pragma comments and the role of Advapi32 library. Many thanks!
