Database Users

data type conversion in eVC++

Hello Everyone
I hope this is not too trivial a question. I am new to eVC. I would like to know how to convert from data type LONG to data type CHAR OR STRING in eVC.
Long myLong=1134.67
In VB the conversion will simply be
myString=STR(myLong)
How can I achieve this in eVC++?
Also someone please recommend some good books on eVC++.
Thanks.
ajanaman

evc++ is just like vc++
which is just like c++ with mfc on top of it
to do simple type casts you do
x=(Type)y;
here are some links also included dynamic type casts
http://www.cplusplus.com/doc/tutorial/typecasting.html
http://www.torjo.com/win32gui/doc/window_casting.html

Hello gsmtexts!
First I would like to point out that in C++ LONG data type is a 4 byte signed integer (in your example you use a floating point value).
Second I assume that by converting you mean representing the number as a string of characters an not just letting the computer assume that the variable contains ASCII values instead of a number.
Here's how you do it:
C++ language doesn't have string data type instead you use an array of char.
Example:
Code:
char myStr[255]; //you have a string of up to 255 ASCII chars.
double myVal = 50.1234; //a double precision floating point value
_gcvt(myVal, 6, myStr); //convert the string
You could use one of the functions (you can search the MSDN site for more details): _gcvt, _ecvt, _fcvt, but there is a simpler way as well:
Code:
WCHAR myStr[255]; //win CE works with Unicode strings.
float myVal = 1.2345; //the value
swprintf(myStr, L"The value: %f", myVal); //creates a string: 'The value: 1.2345'
Finally if you are using MFC:
Code:
CString str;
float myVal = 1.2345;
str.Format(_T("The value: %f"), myVal);
As for books I can only recommend "Teach yourself C++", by Jesse Liberty, it got me started in C++ programming.
Good luck.

Dear levenum
many thanks - I have sratched my head for nearly a week and you gave me the solution just like that. _gcvt did it. u are a wonderful guru.
ajanaman

You are welcome gsmtexts!
But I am far from being a guru. I just like programming so I picked up a book or two and the ball started rolling. 8)
Anyway, since you chose to use _gcvt you should know that in order to use the string you get with windows API's like SetWindowText you will have to convert it to Unicode:
Code:
WCHAR uniBuffer[50]; //Unicode buffer
char myString[50]; //ASCII buffer
_gcvt(1.2345, 5, myString); //convert value to string
mbstowcs(uniBuffer, myString, 50); //convert ASCII string to Unicode

The standard c++ way would be:
double d=122.332;
std:stringstream oss;
oss << d;
std::string mystring=oss.str();

The standard c++ way would be:
double d=122.332;
std:stringstream oss;
oss << d;
std::string mystring=oss.str();

intro!

Hi Guys,
I'm going through the forum, I'm new to embedded developement, I've been able to do my first MessageBox("Hello World") in C using VS2005.
I want to understand how all this works, like :
- Accessing any "mass storage" device ? (the root FS ?, /, c:\, whatevername )
- Dumping the whole registry + values.
- Logging Process and activity even while "device locked" (new process, etc..)
And having more knownledge about the internals and devices, booting etc..
I'm kind of lost and my embedded knowledge is very thin..
The PPC i have is running WM5 on QTEK9100 (SPVM3000)..
Any pointers, posts, sources, small explication are more than welcome...
Hope you can help,
Regards,
r.

Welcome!
Wow those sure are some heavy requests for someone who is just starting.
How much experience do you have with C and Win32 APIs?
To start you off here is an excellent site for Windows Mobile programming tips and tricks:
www.pocketpcdn.com
Couple more pointers:
Device root is "\", no drives (SD cards mounted as folders) kind of like Linux.
All path are absolute - no ".\" or ".."
You can use standard C or Win32 functions for file operations.
Registry functions are also same as Desktop windows except you have to use the "Ex" version of of the function.
Example:
RegOpenKey - not implemented, use RegOpenKeyEx.
For process lists etc, google for ToolHelp32.

Thanks,
I'm at ease w/ ANSI C, have some familiarity w/ Win32 APIs,
but as far as I'm seeing I'm trying to code on Win32 Intel First,
then i try to "port" it to PocketPC Mobile, sometime it works
sometime functions doesn't even exists... MSDN doesn't seems very consistent over Win32 vs WM, but as I'm new I guess i'm missing a lot..
WinMain() prototype changes according to your target...otherwise
VS2005 yell about Overloading WinMain, It is VERY annnoying..anyway
Thanks for the links and the *Ex trick, I'll try to get deeper with this.
I have a strange problem trying to do my Own MessageBoxPrintf:
int MessageBoxPrintf(int, const char * title, const char * fmt, ...)
{
va_list ap;
char * buffer = NULL;
/* formatting and fixed size yes...*/
buffer = (char *) malloc (1024 * sizeof(char));
if (!buffer)
return -1;
memset(buffer, 0, 1024);
va_start(ap, fmt);
vsprintf(buffer, fmt, ap);
va_end(ap);
MessageBox(NULL, (LPCWSTR)buffer, (LPCWSTR)title, type);
return 0;
}
It does compile, but it display craps, since there is no stderr,stdout,stdin and
that I'm mostly coding on Win32/VMware, I don't know how to debug on my PPC (no USB connection), and I have no idea what's wrong.. it might be obvious, but it's late..
As I don't know what LPCWSTR stand for, I assumed char * and it did work on Win32 (XP) without hassle (except LPCWSTR types which are wrong for Win32 Target), so why it doesn't on WM5... is a mystery for me now..
Hope to be on speed ASAP to be able to release some stuff..
Thanks for your help,
Cheers,
r.

all WinAPI function on Pocket PC works with Unicode strings. So you have to convert from ANSI to Unicode.

ok, does the TEXT() macros convert to Unicode string, it seems not.
How to convert from ANSI to Unicode ?

you can work directly with wchar_t or use tchar that can be ansi or unicode, otherwise look for MultiByteToWideChar or CString object _T and TEXT Macro aren't for converting ansi but they makes unicode prefix strings... for example MessageBox(hWnd,_T("Hello World"),_T("my messagebox"),MB_OK);
I hope this help and don't forget MSDN have all replies
have fun,
Guybrush

ok it works! thanks!
just another question, how to dump the "disk" or how those devices are booting ROM?/Flash?
Currently I'm copying all the files from / to the SD card mount point is there anything else?
again thanks for your help.
++
r.

VB.NET how to pass a struct? anyone?

Anyone know how to pass a pointer to a struct in VB.NET that could help me out?
" pGPSPosition
Pointer to a GPS_POSITION structure. On return, this structure is filled with location data obtained by the GPS Intermediate Driver. The dwValidFields member of the GPS_POSITION instance specifies which fields of the instance are valid."
This is from a link on MS site: (http://msdn2.microsoft.com/en-us/library/bb202050.aspx)
So how do I do this in VB?
Looking for a little love here...
TIA,

WM6 SDK contains the sample with the complete wrapper around the GPS intermediate driver in the managed code
But one warning - on some devices (namely HTC Artemis) the serious bug in some version of code provided by Microsoft to Oem return an error when calling functions this API. Communication with a GPS via serial port is still more reliable for a commercial solutions...

Appreciate the response but do you have any source that I can use with VB? My biggest problem is actually retrieving any information from the GPS device using the "GPSGetPosition" function. (see other link - http://forum.xda-developers.com/showthread.php?p=1979418#post1979418)
"But one warning - on some devices (namely HTC Artemis) the serious bug in some version of code provided by Microsoft to Oem return an error when calling functions this API"
Could you be a little more specific?
TW,

Semi manual marshhalling of structure to pointer:
Dim pointerM As IntPtr = Marshal.AllocHGlobal(Marshal.SizeOf(myStruct))
Marshal.StructureToPtr(myStruct, pointerM, False)
Marshal.FreeHGlobal(pnt)
Ad Artemis and another devices) GPS structure has invalid size from old platform builder and intermediate driver (GPS API) refuse it with error.

RStein,
As I was reading about it appeared that Marshaling was going to have to be used in some way since I'm pretty sure that the struct would need to be passed to the C function.
Which brings me to another Q since it appears your are savy at programing in C - how to convert the following C struct?
The struct appears to have a couple of arrays and a few other enums thats are passed to the function, how is that handled in VB?
DWORD GPSGetPosition(
HANDLE hGPSDevice,
GPS_POSITION *pGPSPosition,
DWORD dwMaximumAge,
DWORD dwFlags
);
typedef struct _GPS_POSITION {
DWORD dwVersion;
DWORD dwSize;
DWORD dwValidFields;
DWORD dwFlags;
SYSTEMTIME stUTCTime;
double dblLatitude;
double dblLongitude;
float flSpeed;
float flHeading;
double dblMagneticVariation;
float flAltitudeWRTSeaLevel;
float flAltitudeWRTEllipsoid;
GPS_FIX_QUALITY FixQuality;
GPS_FIX_TYPE FixType;
GPS_FIX_SELECTION SelectionType;
float flPositionDilutionOfPrecision;
float flHorizontalDilutionOfPrecision;
float flVerticalDilutionOfPrecision;
DWORD dwSatelliteCount;
DWORD rgdwSatellitesUsedPRNs[GPS_MAX_SATELLITES];
DWORD dwSatellitesInView;
DWORD rgdwSatellitesInViewPRNs[GPS_MAX_SATELLITES];
DWORD rgdwSatellitesInViewElevation[GPS_MAX_SATELLITES];
DWORD rgdwSatellitesInViewAzimuth[GPS_MAX_SATELLITES];
DWORD rgdwSatellitesInViewSignalToNoiseRatio[GPS_MAX_SATELLITES];
} GPS_POSITION, *PGPS_POSITION;
Click to expand...
Click to collapse
I had a suggestion to create a library from the C# SDK, how difficult would that be? Would it be easier than trying to convert to VB?
Can you help with that?
Thanks for any feedback...

Calculations At Lower Level?

Is there any way to force certain calculations to be done out of the VM? Basically I have algorithms (math) in a program that are slow as balls in Java and would really like if it went faster. I optimized it the best that's really possible, plus Java does some optimizations, but it's still way too slow.
Any way I can kick these calculations off to C land and get things done quicker? I mean my phone's not the fastest (1Ghz Hummingbird), but it should be pretty quick. The JVM is slowing it down by leaps and bounds.
Anybody know anything?
TIA

You can use the NDK to write C code.
Can you provide an example of your problems, though?

hrk said:
You can use the NDK to write C code.
Can you provide an example of your problems, though?
Click to expand...
Click to collapse
Ah, NDK looks like it is exactly what I'm looking for. Looks like the C aspect has to be kind of jammed in there, but I kind of need the performance, so I don't really mind.
As for an example, the program is an image manipulator, so there's many loops. While not a direct pull from my code, an example could be something like this:
Code:
int i, j;
int height = bmp.getHeight();
int width = bmp.getWidth();
int color = 0xFFFF0000;
int count = 0;
for (i = 0 ; i < width ; ++i) {
for (j = 0 ; j < height ; ++j) {
bmp.setPixel(i, j, color);
switch(count % 3) {
case 0:
color = 0xFF00FF00; break;
case 1:
color = 0xFF0000FF; break;
case 2:
color = 0xFFFF0000; break;
}
count++;
}
}
So I do still need access to things (the bitmap) up in Java land.
I see that NDK passes some environment stuff (a pointer to a JNIEnv struct/class, and a copy of a jobject come with each function call, aside from any additional parameters somebody wishes to use). Do you know what those are? I mean I get that one's a pointer to the Java native interface environment, and I'm assuming the object copy is a copy of the object called on it? And types in C land are prefixed with a 'j'?
Thanks for your time and help!

I haven't used JNI in the last... ten?... years, so my memory is a bit dusty there.
In JNI you don't use C-types, but those "J prefixed types" which internally handle all the compiler-platform-java specific differences (simple example: how big is a "long" on an ARM, ia32 and ia64 computer? A jlong has the same size on all of them).
I recommend you these two links: Java programming with JNI (IBM developer network) and Wikipedia: Java Native Interface. I'm not joking, Wikipedia has some basic examples and links to useful informations!
Having said that... can't you go for a different approach, like...
Code:
int[][] rawData = new int[bmp.getWidth(), bmp.getHeight()];
...
for (int i ...) {
for (int j ...) {
// color from switch
// ...
rawData[i][j] = color;
}
}
bmp.somehowSetRawDataInOneCall(rawData);
I don't know which image manipulating class you're using (and I don't know how specific your code was!), but I clearly remember using "mass"-setting methods in one of my projects to speed things up after trying myself your setColor(i, j, color) approach.

hrk said:
I haven't used JNI in the last... ten?... years, so my memory is a bit dusty there.
In JNI you don't use C-types, but those "J prefixed types" which internally handle all the compiler-platform-java specific differences (simple example: how big is a "long" on an ARM, ia32 and ia64 computer? A jlong has the same size on all of them).
I recommend you these two links: Java programming with JNI (IBM developer network) and Wikipedia: Java Native Interface. I'm not joking, Wikipedia has some basic examples and links to useful informations!
Having said that... can't you go for a different approach, like...
Code:
int[][] rawData = new int[bmp.getWidth(), bmp.getHeight()];
...
for (int i ...) {
for (int j ...) {
// color from switch
// ...
rawData[i][j] = color;
}
}
bmp.somehowSetRawDataInOneCall(rawData);
I don't know which image manipulating class you're using (and I don't know how specific your code was!), but I clearly remember using "mass"-setting methods in one of my projects to speed things up after trying myself your setColor(i, j, color) approach.
Click to expand...
Click to collapse
Yeah, using a raw buffer will definitely alleviate some of the overhead simply by removing function calls from the task loop. I'm using the Bitmap class, it has a setPixel method. I'm sure there's a way to dump a new buffer in there. That would definitely speed things up.
Good to know the types are standard sizes, unlike C/C++.
I'll look into the links above, and yes, I trust Wikipedia for all things factual. Not like I'm looking up political stuff there, math and CS is pretty set in stone.
That being said, while it will definitely remove some of the overhead to modify a primitive data structure, that was a fairly simplistic example. The problem is that some of the filters do multiple passes, multiple filter applications, and are in general more complex. I don't believe Java will prove quick enough.
I'll give it a whirl, though, I'll see what happens, maybe I can get some times. I'll post back at some point (few days) when I get time to test it (too busy atm).
Thanks for your time, I'll get back to ya.

DataManagement Library for Easy Android Database Storage

Storing objects to a Database for an Android application should be fast and easy as:
Code:
dm.add(new StorableClass());
DataManagement is a new open source library that allows you to do just that.
DataManagement is a Java Android library designed to help easily and efficiently store aggregate classes to an SQLite database. It eliminates the need to write separate classes to manage database – object interactions and allows developers to use simple methods to store, query, update, and delete objects. The library is capable of storing all objects of classes whose instance variables are either primitive data types or are themselves objects of another storable class. The DataManagement Library condenses many standard database features into several simple methods. It is fully open source and the code can be found at http://epsilonlabsllc.github.com/DataManagement
Examples:
Creating a Storable Class:
Code:
public class StorableClass{
@Id
private int ident;
private int num1;
private double num2;
private String num3;
private boolean num4;
public static final int num5 = 3;
private OtherStorableClass[] ds2;
}
A storable class must meet two requirements. First, the class must have a private instance variable of type int that will be used as the id number of the object. This variable may be read by the application, but the application should not have the capability to write to or change this variable in anyway. This variable is identified by the system with an @Id annotation. In addition, the class should not have any instance variables that are not either primitive types, strings, or other storable objects.
Instantiating a DataManager Object:
Code:
DataManager dm = new DataManager(context);
The open method accepts the calling Context that is going to use the database. Usually this should be the calling Activity.
Opening a Database for Use:
Code:
dm.open();
This method must be called before the database is used in any way.
Closing a Database After Use:
Code:
dm.close();
This method should be called after all database operations have been performed.
Adding an Object to the Database:
Code:
int id = dm.add(new StorableClass());
The add method accepts an object of a storable class as its only parameter and adds it to the database. It returns its id in the database for future use.
Retrieving a Specific Item from the Database by ID:
Code:
StorableClass storableObject = dm.get(StorableClass.class, id);
The get method accepts two parameters: the data type of the stored object and the Id number of the object (the return value of the add method).
Retrieving All Objects of a Given Type Stored in the Database as a Collection:
Code:
storableObjectCollection = dm.getAll(StorableClass.class);
The getAll method’s only parameter is the class of the objects that should be retrieved.
Retrieving a Collection of Storable Objects that match a given criteria:
Code:
Collection<StorableClass> storableObjectCollection = dm.find(StorableClass.class, 5, "num1");
The find method accepts three parameters: the data type of the stored object, the value that is being searched for, and the name of the instance variable as a string. This method is overloaded in such a way that the second parameter may be any primitive value or a string.
Updating an Object in the Database:
Code:
dm.update(id, updatedObject);
The update method accepts two parameters: The id number of the object being updated and the updated object that will replace the existing one I the database. If the id number of the new object and the id number given as the first parameter do not match, the object’s id will be overwritten.
Deleting an Object by its Id number:
Code:
dm.delete(StorableClass.class, id);
The delete method accepts two parameters: The data type and id number of the object to be deleted.
Additional Notes:
Id numbers are used by the database to ensure that objects are put in the correct place and to allow the program to access these objects. It is important that programs using this library do not attempt to set these variables as they will be initialized and managed by the library. These id numbers are unique for objects of a given type; objects of different types may have the same id number. In addition, if objects are deleted from the database their id numbers are left empty and are not reused.
Licensing:
DataManagement is Currently Licensed under the GNU General Public License, version 3 (GPL-3.0). It is intended for open source use by anyone who would like to use it.

This is awesome!!
Tried it out for an app today-- incredibly simple! For those looking-- this library essentially replaces loads of SQL helper classes and queries with an interface that's similar to ArrayList.
Definitely going to use this for everything in the future!
Thanks

Did you change the license or something? The repo is no longer on github.

regaw_leinad said:
Did you change the license or something? The repo is no longer on github.
Click to expand...
Click to collapse
After a quick search on github, it looks like it's been moved here
https://github.com/epsilonlabsllc/DataManagement

cmike21 said:
After a quick search on github, it looks like it's been moved here
https://github.com/epsilonlabsllc/DataManagement
Click to expand...
Click to collapse
Thanks. I forgot to change it. I just edited my post with the correct url.

Sounds awesome! Great work.
Gonna try it this evening.

Anyone compared the performance with db4o?

are there any performance test with other DB libraries for android? and what about the this lib vs contentproviders?
activeandroid.com
code.google.com/p/orm-droid]orm-droid
satyan.github.com/sugar/

will definitly be using this once i learn some app development! thanks for this!

Just in time...

Hello,
I'm trying to build a simple project the test and learn how this lib works, but I'me quite new in programming and I have some difficulties to understand how to use dm.
The project will be a simple song database with edittexts for song and artist. I created the storableClass as the example, but I cannot understand how to connect it with the main activity, so I can use the output of the editTexts.
1st question is: do I need to have the String variables as private? I'm thinking that must have them as public, so I can connect them with the editTexts output.
2nd: question: all these methods needed to be called from storableClass, or from main activity, after I connected the storableClass with main activity? And how I do this?
Probably with the use of context you descibed, but I cannot understand how to do it. I tried sometimes but always get errors and a specific one "The constructor DataManager(Context) is not visible".
Is there any example project' source code which use this lib to get an Idea, or can you explain the context step more extensively?
Thanks in advance and sorry for noob questions.

dancer_69 said:
Hello,
I'm trying to build a simple project the test and learn how this lib works, but I'me quite new in programming and I have some difficulties to understand how to use dm.
The project will be a simple song database with edittexts for song and artist. I created the storableClass as the example, but I cannot understand how to connect it with the main activity, so I can use the output of the editTexts.
1st question is: do I need to have the String variables as private? I'm thinking that must have them as public, so I can connect them with the editTexts output.
2nd: question: all these methods needed to be called from storableClass, or from main activity, after I connected the storableClass with main activity? And how I do this?
Probably with the use of context you descibed, but I cannot understand how to do it. I tried sometimes but always get errors and a specific one "The constructor DataManager(Context) is not visible".
Is there any example project' source code which use this lib to get an Idea, or can you explain the context step more extensively?
Thanks in advance and sorry for noob questions.
Click to expand...
Click to collapse
Here is a sample project: https://github.com/epsilonlabsllc/D.../net/epsilonlabs/datamanagementefficient/test
(It's in the github project.)
You can set the strings on private, because you can grab the values of the edittext on your layout. Eclipse should generate your set/ get methods if you create your private strings. The methods. Take the values and insert them into your db, Look at the sample:
Code:
public DataSample(){
num1 = 3;
numderp = 3.0;
num3 = "three";
num4 = true;
ds2depier = new ArrayList<DataSample2>();
ds2depier.add(new DataSample2());
ds2depier.add(new DataSample2());
}
That is the basic constructor of the DataSample class. If you do an insert like
int id = dm.add(new StorableClass());
Click to expand...
Click to collapse
The basic constructor will be called and it sets your values for example the num1 =3. You could overwrite the basic constructor with your costum constructor to insert your values.
You activity call:
dm.add(DataSample(sSong,sTitle));
Click to expand...
Click to collapse
The constructor could be something like this:
public DataSample(String sSong, String sTitle){
sYourTitleDataBaseColumnCaption = sTitle;
sYourSongDataBaseColumnCaption = sSong;
}
Click to expand...
Click to collapse
Or use the set/get methods, my custom constructor are just an idea to show you an example. Just take a closer look at the github sample and it should work for you.

Thanks, I think I can figure it out now.

How to is very outdated. I can't initialize via new DataManager() but via getInstance(), also delete and update method doesn't have Id argument anymore.
Also,
I can't get this to work. I can't even add a member to collection because it needs to use db.add(new MyClass()); but i already have MyClass() initialized with their members. I have tried to do something like copy the Id from add, update into my other instance of this class and run a db.update() but it throws a RuntimeException.
Not usable at this time.

Sounds good!
I'll give it a try as soon as I start a new project that requires data storage ...
I really hate SQLiteOpenHelper, cursor and all this strange syntax ...

The idea is good, but it can't be compared to db4o, specially when talking about documentation.

Hello mate,
I'd like to use your library and backup the data with Google/Dropbox Sync... can you tell me the name of the file on which you save data?
Thanks,
Tiwiz