Android (Java) Learning Note 258:jni hello.c (c code function Implementation) Pointer syntax parsing

1. Let's take a look at the code for the implementation of the C feature in the previous lecture:

(1) HELLO.C:

1#include <jni.h>2 3 Char*Gethello ()4 {5     ////////6     return "Hello Android from C";7 }8 9 Ten //JNI protocol to Java calls One //return type method name (Java_ package name (using "_" to split the package name) _ Class Name _ Method name (parameter) A  - //jnienv* ENV JNI structure data, JNI system implementation; Obj Java object calls the object of the Jni method -Jstring JAVA_COM_HIMI_HELLOWORLD_MAINACTIVITY_GETHELLOFROMC (jnienv*env, Jobject obj) the { -     Char* res = Gethello ();//get to C code string result -     /** - * (**env). GetVersion (env); + * (*env)->getverison (env); -      */ +     //jstring (*newstringutf) (jnienv*, const chat*); AJstring JREs = (* *env). Newstringutf (env,res); at  -     returnJREs; -}

jstring : Data type is void* (pointer to an empty area, initialized)

Under the jni.h file:

typedef void* Jobject;

typedef jobject Jclass;

typedef jobject Jstring;

• jnienv* env :

Jninativeinterface struct: Description jninativeinterface is a struct

typedef const struct JNINATIVEINTERFACE* jnienv;: Description jnienv is a struct pointer (this struct is jninativeinterface)

This time jnienv* env is equivalent to:

jninativeinterface** env;: That is, the Env is defined as a pointer to a struct pointer (double pointer)

If you want to use Env to access the members of the Jninativeinterface struct newstringutf ( except Newstringutf Here is a function pointer ) .

(**env). NEWSTRINGUTF (jnienv*, const char*);

Android (Java) Learning Note 258:jni hello.c (c code function Implementation) Pointer syntax parsing