I searched online and on this site and found this link which asks the same question I am about to, but the reply does not seem address the question. Plus one of the referenced links are missing. Basically the question is how do you efficiently and intelligently decide when to use a jni-compatible function to what you have in your C source file. I am familiar with what javah command does, but that command converts JAVA methods into a C header file to be used. What about the methods that are already implemented in a C source file? How can you know if you have to convert them to a JNI version of the method? I am using Android Studio and put in the following code in the .c source file that is in my jni folder of the project:
#include "com_example_sansari_usetbt_MainActivity.h"
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <android/log.h>
#define TAG "native-log-tag"
#define LOGI(LOG_TAG, ...) __android_log_print (ANDROID_LOG_INFO, TAG, __VA_ARGS__)
#define LOGV(LOG_TAG, ...) __android_log_print (ANDROID_LOG_VERBOSE, TAG, __VA_ARGS__)
#define LOGE(LOG_TAG, ...) __android_log_print (ANDROID_LOG_ERROR, TAG, __VA_ARGS__)
/*
* Class: com_example_sansari_usetbt_MainActivity
* Method: usetbt
* Signature: ()Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_com_example_sansari_useqsee_MainActivity_Usetbt
(JNIEnv *env, jobject obj)
{
int fd;
int rc = 0;
char *rd_buf[16];
//(*env)->printf("<1>%s: entered\n", argv[0]);
printf("<1>: entered\n");
fd = open("/dev/tbt", O_RDWR);
LOGI(LOG_TAG,"This is a log test");
LOGV(LOG_TAG,"This is a log test");
LOGE(LOG_TAG,"This is a log test");
//(*env)->fd;
//return;
if ( fd == -1 ) {
perror("<1>open failed");
rc = fd;
}
printf("<1>: open: successful\n");
/* Issue a read */
rc = read(fd, rd_buf, 0);
//I need to find what fd is and then use command completion to pick a jni finction. rd-buf seems to be jstring, and 0 seems to be int
rc = (*env)->GetString
if ( rc == -1 ) {
perror("<1>read failed");
close(fd);
}
printf("<1>: read: returning %d bytes!\n",rc);
close(fd);
(*env)->NewStringUTF(env,"Hi From Usetbt version 2");
}
And ndk-build compiles the project, but I do not get the result I am looking for. That is, the normal C version of the code which I compiled with NDK opens the driver and is able to interface with it, but this does not do the same. I do not see the result of the print statement in the kernel logs that is. I am not asking for someone to convert the above code; rather show me the way to know which of the above lines need to be converted, and what is the best way to do it please. I have read a number of items about this, and I am quickly coming up to speed, but if you can describe at a high level how
this conversion is done, please advise. I do have a copy of Java Native Interface and a number of Android texts and am going through them as fast as possible.
Thanks
I believe you need to call fflush(stdout); after your printf. As per this answer.
Related
I am trying to load a file in NDK using ifstream but it fails to read it. I've double checked the path of the file and it is not wrong. The same program works in normal C++(without the JNI stuff ofcourse).
#include <jni.h>
#include <string>
#include <iostream>
#include <istream>
#include <sstream>
#include <fstream>
using namespace std;
extern "C"
{
JNIEXPORT jstring JNICALL Java_com_example_aaaaatrytest_MainActivity_stringFromJNI(JNIEnv *env, jobject /* this */) {
string file_path = "/home/moe/Desktop/blah.txt";
std::ifstream fim(file_path);
if(fim.is_open())
{
string pass = "File Loaded";
return env->NewStringUTF(pass.c_str());
}
else{
std::string fail = "Failed to load file";
return env->NewStringUTF(fail.c_str());
}
}
}
After removing if-else and debugging, this is what debugger displays:
SIGTRAP (signal SIGTRAP)
env = {JNIEnv * | 0x55bc7ccc00} 0x00000055bc7ccc00
{jobject | 0x7fcefb1af4} 0x0000007fcefb1af4
I have tried to use fstream instead of ifstream but same error. I've also provided external storage write and read permission in manifest.xml but it didn't help.
This problem is format independent as I've tried to put different files in the path. Why is it failing to read the file?
l have copied the file to my device and gave android path but it still fails to read. My android's path to file looks like this "/storage/emulated/0/abc/abc.txt".
Your app needs READ_EXTERNAL_STORAGE permission.
Here is a small snippet that helps to request this permission at runtime: see READ_EXTERNAL_STORAGE permission is in manifest but still doesn't work.
I'm trying to use short[] and jshortArray between C/JAVA as follows in Eclipse:
JNIEXPORT void JNICALL Java_com_testingForFun_testFunc
(JNIEnv *env, jclass clazz, jshort num, jshortArray data) {
jshort outCArray[] = {100, 200};
jshortArray outJNIArray = (*env)->NewShortArray(env, 2); // allocate
if (NULL == outJNIArray) return;
(*env)->SetShortArrayRegion(env, outJNIArray, 0 , 2, outCArray); // copy
//return outJNIArray;
}
I've created the header file using javah and included it. However, Eclipse says NewShortArray and SetShortArrayRegion are unresolved and I can't build the apk. However, not using arrays (jshort and short) works fine. I looked in jni.h and it seems that NewShortArray other related functions are defined if __cplusplus is defined, but I'm using C. I also built the apk on the command line using ndk-build and ant and I read outJNIArray[0] or [1] = 0 in the calling function, so it's not working there either. How do I resolve this issue?
Additionally, Eclipse can't resolve ANDROID_LOG_DEBUG in:
__android_log_print(ANDROID_LOG_DEBUG, "FibLib.c", "fibNI(%lld)", n);
even though
#include <android/log.h>
is at the beginning of the file.
I used Eclipse restart and seems to have cleared up these issues. But every time I edit my .c file, the unresolved errors pop up, and I need to restart. It's very annoying. Any fix for this?
The issue of outJNIArray[] not being set is a separate topic, so I will ask another question on the forum in the future if necessary.
I'm writing an Adroid app with some C++ code behind the UI using Eclipse + NDK (r8d). I have some code that I thought was fool proof but the compiler just gives me weird errors like "Invalid arguments" without specifics. Here is what my C++ code looks like:
#include <jni.h>
#include <string>
using namespace std;
#include "../../Evaluator.Engine/Evaluator.Engine.h"
Evaluator evaluator;
extern "C" {
JNIEXPORT jstring JNICALL Java_haskellevaluator_android_MainActivity_evaluateNative(JNIEnv *env, jobject, jstring jInput)
{
...
string sInput(L"Hello world");
string sResult = evaluator.evaluate(sInput);
jstring jResult = env->NewStringUTF(sResult.data());
return jResult;
}
}
Evaluator.Engine.h is nothing fancy, but just a declaration of the class Evaluator.
#include <string>
using namespace std;
class Evaluator
{
public:
string evaluate(string input);
};
However, the compiler complains:
Invalid arguments '
Candidates are:
? evaluate(?)
'
as if string is not defined. But if I put a copy of the header file under the same folder, the error goes away. This is a Windows box. I have tried using \ and escaped \\ as path separators and it didn't work.
Does this sound like a NDK (or whatever the preprocessor it uses) bug? I don't want to move the header file because it'll be shared by other projects. I also hate to keep 2 copies of the same file.
Any ideas? Thanks.
Sorry I don't have windows OS, but I've tried you code on a MacOS, but it doesn't work because of:
string sInput(L"Hello world");
Saying that wchar_t cannot be put on std::string. Is it possible to be the same problem ?
I've just installed the NDK onto Eclipse, but I'm having some trouble with something..
Here's the code:
#include <jni.h>
#include <stdlib.h>
#include <stdio.h>
void deleteFile(const char *fileName) {
remove(fileName);
}
void writeFile(const char *fileName, byte array) {
}
But something is going wrong.. I got this error:
jni/[projectName].cpp:9:38: error: 'byte' has not been declared
byte couldn't be resolved! which is a big problem because I absolutely need that type.. I have to use it to write data into a file!
I've followed a lot of tutorials, I also tried to import all of my MinGW libraries with no success.
byte isn't a standard C or C++ type ... It may be a typedef in a non-standard header file. Where have you seen code with that type ? May be you would like to use const unsigned char * ?
I know that Visual Studio define BYTE type:
typedef unsigned char BYTE; // 8-bit unsigned entity.
typedef BYTE * PBYTE; // Pointer to BYTE.
But this is not standard. And it is "BYTE", not "byte".
'byte' doesn't exist in standard C or C++, if all your code depends on , use 'jbyte' instead, it is defined in this header, and maps to an 8-bit unsigned integer type.
Alternatively, you could define 'byte' with a typedef as in:
typedef unsigned char byte;
And ensure this is used/parsed by all your sources (e.g. put it in a shared header).
A slightly more correct way to do it is:
#include <inttypes.h>
typedef uint8_t byte;
It will be equivalent on all supported Android platforms, but requires an additional include.
(Technically, 'char' can be more than 8 bits on some really odd platforms, but none of them are ever going to be targetted by Android).
I like to build the Android NDK example "native-audio", supplied with the NDK.
The NDK-supplied compiler swallows it without complaint, but Eclipse is showing several errors in file native-audio-jni.c.
In the code excerpt below, all of the static variable declarations have red underlining, because Eclipse claims that the types cannot be resolved. They are defined right up there in the OpenSLES.h file, which Eclipse does find if I Ctrl + left click the file.
Note that I modified the lines where hello_clip and android_clip are included compared to the example source - I put the array declarations in those "header" files also (they contained just comma separated data), since Eclipse had a problem parsing the syntax, too:
static const char array[] = #include"blah.h";
I tried things suggested over the internet, like starting with eclipse.exe -clean, clean project / rebuild, refresh project, etc., none helps.
So, what could be the reason/solution for Eclipse not resolving those types?
#include <assert.h>
#include <jni.h>
#include <string.h>
// for __android_log_print(ANDROID_LOG_INFO, "YourApp", "formatted message");
// #include <android/log.h>
// for native audio
#include <SLES/OpenSLES.h>
#include <SLES/OpenSLES_Android.h>
// for native asset manager
#include <sys/types.h>
#include <android/asset_manager.h>
#include <android/asset_manager_jni.h>
// pre-recorded sound clips, both are 8 kHz mono 16-bit signed little endian
// includes data arrays here
#include "hello_clip.h"
#include "android_clip.h"
// engine interfaces
static SLObjectItf engineObject = NULL;
static SLEngineItf engineEngine;
// output mix interfaces
static SLObjectItf outputMixObject = NULL;
static SLEnvironmentalReverbItf outputMixEnvironmentalReverb = NULL;
(the file is full of many more of those problems)