Develop Reference

How to find out the full directory of a file in Android phone to be used with fstream?

I am trying to test a very basic c++ code in CppDroid app to create a text file on my Android phone (Huawei P20pro). But it doesn't seem to work. I think the problem is with the file directory. Can someone let me know how to get the real full directory of a file/folder in Android phone?
#include <iostream>
#include <fstream>
using namespace std;
int main ()
{
ofstream NewFile;
NewFile.open("/Internal Storage/CppDroid/projects/project_dec23a/Gyrocopter.txt");
NewFile << "This is a file about a gyrocopter. \n";
NewFile.close();
return 0;
}

undefined lame decode function

I'm trying to add MP3 read and write capabilities to my Android app. I'm using the lame4android app as a starting point. Encoding a file works for me, but I'm having a problem with the decode functions -- I'm getting undefined references to the decode functions.
Here are excerpts from my wrapper.c:
#include "libmp3lame/lame.h"
#include "jni.h"
lame_t lame;
jint Java_com_intonia_dandy_WavStream_initEncoder(JNIEnv *env,
jobject jobj,
jint in_num_channels,
jint in_samplerate)
{
lame = lame_init();
...
return lame_init_params(lame);
}
hip_t hip;
jint Java_com_intonia_dandy_WavStream_initDecoder(JNIEnv *env, jobject jobj)
{
hip = hip_decode_init();
return hip != 0;
}
And here are the declarations from lame.h:
lame_global_flags * CDECL lame_init(void);
typedef hip_global_flags *hip_t;
hip_t CDECL hip_decode_init(void);
I'm getting an error message:
C:/ACode/dandy/src/main/jni/./wrapper.c:62: undefined reference to `hip_decode_init`
I'm also getting undefined references to hip_decode and and hip_decode_exit. But lame_init, lame_init_params, lame_encode_buffer, and lame_encode_flush do not generate any errors. I get these errors using the command line to run ndk-build, and I get the same errors when I let Android Studio manage the compilation.
How are the lame_* functions different from the hip_decode_* functions? Should I be using the deprecated lame_decode_*?
EDIT: I'm looking at the output of the ndk-build command. The .c files are listed on the console as they are compiled. hip_decode_init is defined in jni/libmp3lame/mpglib_interface.c, but mpglib_interface is not getting compiled, even though it's listed in jni/Android.mk. Why not???

It turns out that the LAME library as distributed does not have decoding enabled. To get it working, I had to do the following:
Add #define HAVE_MPGLIB 1 to mpglib_interface.c
Copy all .c and .h files from the mpglib directory of the LAME distribution.
Edit Android.mk to include the .c files from mpglib.
EDIT: instead of modifying mpglib_interface.c to define HAVE_MPGLIB,
it's better to set compilation flags.
Working with Android Studio 2+, build.gradle should contain
android {
defaultConfig {
ndk {
moduleName "libmp3lame"
cFlags "-DSTDC_HEADERS -DHAVE_MPGLIB"
}
}
}
Or in Android.mk:
LOCAL_CFLAGS = -DSTDC_HEADERS -DHAVE_MPGLIB

how to convert C code to JNI compatible C code?

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.

NDK unable to deal with #include with relative paths?

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 ?

Crashing when loading zip using cocos2d-x

I have a problem using cocos2d-x on android.
I am trying to load a .zip file using
CCFileUtils::sharedFileUtils()->getFileDataFromZip(...)
As this project is designed to be multiplatform, we also tried this code on an iPad3 and there it is working without problem.
The problem is that the app gets an Segmentation Fault when loading the zip file.
Here is the whole code with some extra comments
void Map::loadChunk(int index, CCPoint startPoint) {
chunks[index]->startPoint = startPoint;
std::stringstream filename;
filename << (int)startPoint.x << "_" << (int)startPoint.y << ".map";
unsigned long filesize = 0;
const char* path = CCFileUtils::sharedFileUtils()->fullPathFromRelativePath("map1.zip");
CCLog(path);
CCLog(filename.str().c_str());
// In the following two lines the error occurs
const char* buffer =(const char*) CCFileUtils::sharedFileUtils()->getFileDataFromZip(path, filename.str().c_str(), &filesize);
std::istringstream fileBuffer(buffer);
CCLog("filesize %d", (int)filesize);
std::string line;
// Here some code follows but this code does not produce the problem so I left it out
}
The used includes are:
#include <iostream>
#include <fstream>
#include <sstream>
#include <map>
#include "cocos2d.h"
The values for path and filename are
map1.zip and -128_-128.map
map1.zip is in the assets folder and the .map file exists inside map1.zip
Thanks in advance

I've figured out why this is not working.
It seems to be the problem to pack another .zip into the .apk.
When playing the .zip in the folder received by
CCFileUtils::sharedFileUtils()->getWriteablePath()
and then open the zip with
CCFileUtils::sharedFileUtils()->getFileDataFromZip(...)
the zip loads properly and I am able to read certain files from inside the zip.