JNI programming tips (continuous update)

1. The string passed in by Java is converted to char * in C and printed

Jstring OBJ;

Const char * string = (char *) (* env)-> getstringutfchars (ENV, OBJ, null );

_ Android_log_print (android_log_info, "jnimsg", string );

2. The 'for' loop initial declarations are only allowed in c99 mode Error

Int I = 0;

For (; I <size; I ++ ){}

Int I needs to be defined before

3. Obtain the Elements marked as I in the array.

Jobject OBJ = (* env)-> getobjectarrayelement (ENV, array, I ));

4. JNI defines the string array and assigns a value to the string array.

Jobjectarray arrays = 0;
// Define the length
Jsize Len = 20;
Arrays = (* jnienv)-> newobjectarray (jnienv, Len, (* jnienv)-> findclass (
Jnienv, "Java/lang/string"), 0 );

Jstring jstr;
Char * Sa [] = {"hello,", "World! "," JNI "," very "," fun "};
Int I = 0;
For (; I <Len; I ++)
{
Jstr = (* env)-> newstringutf (ENV, sa [I]);
(* Env)-> setobjectarrayelement (ENV, arrays, I, jstr); // jstring must be included
}

5. Obtain the array value

Int K = 0;
For (; k <Len; k ++ ){
Jstring string = (jstring) (* jnienv)-> getobjectarrayelement (jnienv,
Arrays, k ));
If (string! = NULL ){
Char * c = (* jnienv)-> getstringutfchars (jnienv, String, 0 );
_ Android_log_print (android_log_info, "jnimsg", C );
}
}

6. intermediate layer data type conversion

char * ---> jstring (* jnienv)-> newstringutf (jnienv, char *)
jstring ---> char (* jnienv)-> getstringutfchars (jnienv, jstring, 0);
long ---> char * ltoa (long, char *, 10); sprintf (csendbodylen, "% lD", sendbodylen );
char * ---> long * long = atol (char *);