How to convert between Android JNI and Java data transfer

The jstring data type in 1.c is the Java incoming string object, and the conversion of the JNI function can become the char* of C.

java		local C type	description
boolean	jboolean	unsigned	8 bit
byte	jbyte	unsigned	8 bit
char	jchar	unsigned	16 bit
short	jshort	signed	16 bit
int	jint	signed	32 bit
long	jlong	signed	64 bit
float	jfloat	signed	32 bit
double	jdouble	signed	64 bit

2. How do I convert a Java-passed string parameter to C's char* and then use the? Java passed in the string parameter, in the C file by Jni converted to jstring data type, in the C file declared char* test, and thenTest = (char*) (*env)->getstringutfchars (env, jstring, NULL); Note: When test is finished, notify the virtual machine platform that the relevant code is no longer accessible:(*env)->releasestringutfchars (env, jstring, test);3. Pass a char* buffer obtained in C to Java?     This char* if it is a generic string, it can be passed back as a string. If it is a buffer containing '/0 ', it is best to pass as ByteArray because the length of the copy can be set, and if copy is to string, it may be truncated to '/0 '. There are two ways to pass the resulting data: a byte array that is directly new in JNI and then called Functions     (*env)->setbytearrayregion (env, ByteArray, 0, Len, Buffer), copy the value of buffer to ByteArray, and the function will return directly to ByteArray. One is the return error number, the data is passed as a parameter, but the basic data type of Java is a value, and the object is a passing reference, so the byte array that needs to be outgoing is wrapped with a class, as follows:    class retobj{        public byte[] bytearray;   } This object is retobj outgoing as a function parameter The assignment of a byte array in Retobj is facilitated by the following function. The code is as follows:    Jclass cls;    jfieldid fid;    jbyteArray bytearray;     ByteArray = (*env)->newbytearray (Env,len);    (*env)->setbytearrayregion (env, ByteArray, 0, len, buffer);    CLS = (*env)->getobjectclass (env, retobj);    FID = (* ENV)->getfieldid (env, CLS, "Retbytes", "[B"]);    (*env)->setobjectField (env, retobj, FID, ByteArray); 4. How to return a string in C to java    Char charstr[50];    Jstring jstr;  jstr = env-Newstringutf (CHARSTR);5. How much space does not know how to use buffer, how to pass out? In the JNI C file, new out of space, passed out. Java data is not initialized, pointing to the space passed out. Another: the processing of Java incoming data in JNI if the incoming is ByteArray, the following processing gets Buffer:char *tmpdata = (char*) (*env)->getbytearrayelements (env, byte    Array, NULL); (*env)->releasebytearrayelements (env, ByteArray, Tmpdata, 0);

How to convert between Android JNI and Java data transfer