CODEWITHSUNDEEP
androidandroid-ndk
user4435944
user4435944

Reputation:

'NULL' undeclared (first use in this function) using android ndk

I am working on android-ndk in which i try to pass string from my C code to my java and then in activity. My codes are given below but i am getting the following errors. Please help me out here

#include <com_testing_ndk_FibLib.h>

JNIEXPORT jstring JNICALL Java_Sample1_stringMethod(JNIEnv *env, jobject obj,
        jstring string) {

    const char *name = (*env)->GetStringUTFChars(string, NULL); //Java String to C Style string
    char msg[60] = "HelloWorld";
    jstring result;

    strcat(msg, name);
    (*env)->ReleaseStringUTFChars(string, name);
    puts(msg);
    result = (*env)->NewStringUTF(msg); // C style string to Java String
    return result;
}

Error log:

jni/com_testing_ndk_FibLib.c: In function 'Java_Sample1_stringMethod':
jni/com_testing_ndk_FibLib.c:7:55: error: 'NULL' undeclared (first use in this function)
  const char *name = (*env)->GetStringUTFChars(string, NULL); //Java String to C Style string
                                                       ^
jni/com_testing_ndk_FibLib.c:7:55: note: each undeclared identifier is reported only once for each function it appears in
jni/com_testing_ndk_FibLib.c:7:21: error: too few arguments to function '(*env)->GetStringUTFChars'
  const char *name = (*env)->GetStringUTFChars(string, NULL); //Java String to C Style string
                     ^
jni/com_testing_ndk_FibLib.c:11:2: warning: incompatible implicit declaration of built-in function 'strcat'
  strcat(msg, name);
  ^
jni/com_testing_ndk_FibLib.c:12:2: warning: passing argument 2 of '(*env)->ReleaseStringUTFChars' discards 'const' qualifier from pointer target type
  (*env)->ReleaseStringUTFChars(string, name);
  ^
jni/com_testing_ndk_FibLib.c:12:2: note: expected 'jstring' but argument is of type 'const char *'
jni/com_testing_ndk_FibLib.c:12:2: error: too few arguments to function '(*env)->ReleaseStringUTFChars'
jni/com_testing_ndk_FibLib.c:14:11: warning: passing argument 1 of '(*env)->NewStringUTF' from incompatible pointer type
  result = (*env)->NewStringUTF(msg); // C style string to Java String
           ^
jni/com_testing_ndk_FibLib.c:14:11: note: expected 'const struct JNINativeInterface **' but argument is of type 'char *'
jni/com_testing_ndk_FibLib.c:14:11: error: too few arguments to function '(*env)->NewStringUTF'
make: *** [obj/local/arm64-v8a/objs/com_testing_ndk_FibLib/com_testing_ndk_FibLib.o] Error 1

My Java Code:

public class FibLib {

    static {
        System.loadLibrary("com_testing_ndk_FibLib");
    }



     public static native String stringMethod(String text);

        public static void main(String[] args)
        {
           System.loadLibrary("Sample1");
           FibLib sample = new FibLib();

           String  text   = sample.stringMethod("world");

           System.out.println("stringMethod: " + text);    
       }
}

Upvotes: 0

Views: 2869

Answers (2)

ph0b
ph0b

Reputation: 14473

All your JNI calls are missing the first parameter which should be env, as you're in compiling C code.

If your code was in C++, you could make calls like env->NewStringUTF("xx"). But in C, JNIEnv* isn't an object, hence you have to pass it as first argument, like so: (*env)->NewStringUTF(env, "xx")

As for NULL being undefined, you can solve this by including the header that defines it: #include <stddef.h>

Upvotes: 1

Peanut
Peanut

Reputation: 3963

The second parameter does not seem to be optional:

jboolean iscopy;
const char *name = (*env)->GetStringUTFChars(string, &iscopy);

Upvotes: 0

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