使用 JNI 从 Java 调用 C 函数

Question

I have the following C code. My aim is to call a C function from java.

C code:

_declspec(dllimport) BYTE __stdcall  CPSC1900Connect(BYTE port, void *param);



JNIEXPORT jbyte JNICALL Java_CPSE_CPSC1900Connect(JNIEnv * env, jclass hPrinter, jbyte port, jstring Answer)
{

     BYTE RC;

// I need to call CPSC1900Connect(BYTE port, void *param); function and pass (i DONT KNOW HOW TO PASS THOSE PAREMETER TO THIS METHOD.

//port and ANSWER PARAMETER. THE METHOD RETURNS BYTE WHICH I SHOULD BE VIED FROM JAVA

     return Answer;
}

java code:

public class CPSE {

   public  native byte CPSC1900Connect(byte port,String param);
   public  native String CPSC1900Disconnect(String param);
    static{

        try {

            System.loadLibrary("dll/CPSLPT9x");
            System.loadLibrary("dll/CPSRC");
            System.loadLibrary("dll/CPSE");
            System.loadLibrary("dll/MCHIP");


        } catch (Exception e) {
            System.out.println(e);
        }

    }

    public CPSE() {

        byte port=CPSC1900_USB;
                  param ="xx.xx.xx.xx"// ip address
         byte   response= CPSC1900Connect(BYTE port, void *param);


    }

    public static void main(String[] args)
    {
        new CPSE();

    }

}

My question is: How can I pass value from java application and pass it to the C function and get a response?

Answer 1

Have you tried the the straightforward implementation?

JNIEXPORT jbyte JNICALL Java_CPSE_CPSC1900Connect(JNIEnv * env, jclass hPrinter, jbyte port, jstring Answer)
{

    const char* param = (*env)->GetStringUTFChars(env, Answer, 0);
    jbyte res = (jbyte)CPSC1900Connect((BYTE)port, (void*)param);

    (*env)->ReleaseStringUTFChars(env, Answer, param);

    return res;
}

This assume the void* param of CPSC1900Connect is read only, otherwise copy the param string to a local buffer.

I have not compiled this code , just wrote it. Do basic corrections if needed.