Android java传递string类型数据给C

/**
* 把一个jstring转换成一个c语言的char* 类型.
*/
char* _JString2CStr(JNIEnv* env, jstring jstr) {
char* rtn = NULL;
jclass clsstring = (*env)->FindClass(env, "java/lang/String");
jstring strencode = (*env)->NewStringUTF(env, "GB2312");
jmethodID mid = (*env)->GetMethodID(env, clsstring, "getBytes",
"(Ljava/lang/String;)[B");
jbyteArray barr = (jbyteArray) (*env)->CallObjectMethod(env, jstr, mid,
strencode); // String .getByte("GB2312");
jsize alen = (*env)->GetArrayLength(env, barr);
jbyte* ba = (*env)->GetByteArrayElements(env, barr, JNI_FALSE);
if (alen > ) {
rtn = (char*) malloc(alen + ); //"\0"
memcpy(rtn, ba, alen);
rtn[alen] = ;
}
(*env)->ReleaseByteArrayElements(env, barr, ba, );
return rtn;
}

/*
* Class: com_wuyudong_javapassdata_JNI
* Method: sayHelloInC
* Signature: (Ljava/lang/String;)Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_com_wuyudong_javapassdata_JNI_sayHelloInC(
JNIEnv * env, jobject clazz, jstring jstr) {
//调用工具方法把java中的string类型转换成C语言中的char×
char* cstr = _JString2CStr(env, jstr);
int len = strlen(cstr);
int i;
for (i = ; i < len; i++) {
*(cstr + i) += ;
}
return (*env)->NewStringUTF(env, cstr);}

public void passString(View v) {
Toast.makeText(getApplicationContext(), jni.sayHelloInC("hello yudong"), 0).show();
}