Re: ADO.NET : SqlDataReader : I need to assign retrieved value to C++ variable - Managed C++/CLI Discussion Boards

Re: Calling Nishant S; Nick Parker ; anyone RE CString and /clr

Nish Nishant16-Oct-02 19:23

Nish Nishant

16-Oct-02 19:23

Hello Doug

I compiled and ran this program successfully.

<br />
#include <Stdafx.h><br />
#include <cstdlib><br />
#include <atlstr.h><br />
<br />
#using <mscorlib.dll><br />
#using <System.dll><br />
#using <system.data.dll><br />
<br />
using namespace std;<br />
using namespace System;<br />
<br />
int main()<br />
{<br />
CString busNumberSQL[2];<br />
CString bus = "Hello";<br />
busNumberSQL[1] = bus;<br />
Console::WriteLine(busNumberSQL[1]); //shows "Hello" on my console<br />
return 0;<br />
}<br />

I have no idea why it's not working on your box.

Regards,
Nish

Author of the romantic comedy

Summer Love and Some more Cricket [New Win]

Review by Shog⁹
Click here for review[NW]

Re: Calling Nishant S; Nick Parker ; anyone RE CString and /clr

Doug17-Oct-02 11:09

Doug

17-Oct-02 11:09

Nish

Thanx

You are correct

Console::WriteLine(busNumberSQL[1]); //shows "Hello" on my console

works, as does

cout << "busNumberSQL[1] = " << static_cast<lpctstr>(busNumberSQL[1]) << endl;

Just a pity you cannot, in this case set up the Watch window as a debugging tool by itself.

Here is what someone wrote :

Quote

I see what you are talking about. Although it is not really a problem but just the way managed code and the CLR interacts with unmanaged code. When you use unmanaged code such as the case with the CString object in your example, and compile with the /clr, the managed executable makes references to the unmanaged objects internally using pointers to its memory location which falls outside the GC managed memory pool. As you have noticed when placing a watch on the unmanaged CString objects which show up as a __int32 type with a value that points to a memory address.

There is nothing wrong with the example you gave in your email. The program still compiles, and the results it produces is as expected. The nice thing with C++.Net is the power of mixing managed and unmanged code in one executable. The power does not come without a price and that is your managed executable with parts unmanaged code, has the same risks as a completely unmanaged executable. The CLR does not offer any protection or resource management to unmanaged objects. So, use the power carefully.

using your example above, if you add to following line to your code you'll see that it still produces the expected results.

Console::Writeline (busNumberSQL[1]);

or even,

printf ("%s",busNumberSQL[1] );

Unquote

http://www.codeproject.com/managedcpp/adonet_mcpp.asp?msg=311206#xx311206xx

Regards

Doug

Doug

Re: Calling Nishant S; Nick Parker ; anyone RE CString and /clr

Doug17-Oct-02 11:19

Doug

17-Oct-02 11:19

Correction:

cout << "busNumberSQL[1] = " << static_cast(busNumberSQL[1]) << endl;

should read:

cout << "busNumberSQL[1] = " << static_cast<lpctstr>(busNumberSQL[1]) << endl;

PS.

Apologies for the multiple post - the error of my way has been pointed out to me and will not happen again.

Doug

ADO.NET : SqlDataReader : I need to assign retrieved value to C++ variable

Doug13-Oct-02 13:31

Doug

13-Oct-02 13:31

I can get the following to work, the result displaying on the screen:

Console::WriteLine(myReader->GetSqlValue(3));

What I really need to do is to assign the item retrieved to a C++ variable eg.

int halfhrSQL = myReader->GetSqlValue(3);

This gives the C2440 compile error: cannot convert from 'System::Object __gc *' to 'int'.

No matter what cast I use, I cannot get around the error.

Please help if you can.

Thanks, Doug (New Zealand)

Doug

Re: ADO.NET : SqlDataReader : I need to assign retrieved value to C++ variable

Nish Nishant13-Oct-02 15:05

Nish Nishant

13-Oct-02 15:05

Use Convert::ToInt32

public: static int ToInt32(
   Object* value
);

Regards,
Nish

Author of the romantic comedy

Summer Love and Some more Cricket [New Win]

Review by Shog⁹
Click here for review[NW]

Re: ADO.NET : SqlDataReader : I need to assign retrieved value to C++ variable

Doug13-Oct-02 18:15

Doug

13-Oct-02 18:15

Hi Nish

Thanks very much for pointing me in the right direction!

I now have the code working:

int halfhrSQL = Convert::ToInt32(myReader->GetValue(3));

It took me a while too find out I had to use GetValue().
Not GetSqlValue(3).
Not GetSqlInt32(3).
Not GetData().
Not GetInt32().

The above compile but throw the following exception:

"System.InvalidCastException : Specified cast is not valid at System.Convert.ToInt32(Object value)"

Best regards

Doug

Doug

Re: ADO.NET : SqlDataReader : I need to assign retrieved value to C++ variable

Nick Parker14-Oct-02 8:19

Nick Parker

14-Oct-02 8:19

Doug if you are still having a problem you might want to read this[^]
article from MSDN, especially the remarks. Smile | :)

Nick Parker

The greatest lesson in life is to know that even fools are right sometimes. - Winston Churchill

Re: ADO.NET : SqlDataReader : I need to assign retrieved value to C++ variable

Doug14-Oct-02 10:17

Doug

14-Oct-02 10:17

Thanks everyone, problem solved!;)

Doug

Re: ADO.NET : SqlDataReader : I need to assign retrieved value to C++ variable

Doug16-Oct-02 12:40

Doug

16-Oct-02 12:40

Hi Nick

Re: ADO.NET : SqlDataReader : I need to assign retrieved value to C++ variable

I have found the source of the problem expressed in the thread "ADO.NET : SqlDataReader : I need to assign retrieved value to C++ variable":
http://www.codeproject.com/script/comments/forums.asp?forumid=3785#xx309754xx

but do not yet know why it occurs or how I can fix it.

The problem arises with the /clr compiler setting.

Here is the code to illustrate this:

/////////////////////////////////////////////////////////

#include <stdafx.h>
#include <cstdlib>
#include "try_ADONET.h"

//#using <mscorlib.dll>
//#using <system.dll>
//#using <system.data.dll> // This is required for the ADO.NET Provider

using namespace std;
//using namespace System;

int Main()
{
CString busNumberSQL[2];
CString bus = "Hello";
busNumberSQL[1] = bus;

return 0;
}

////////////////////////////////////////////////////////

Without the /clr setting the array of CString busNumberSQL[2] is correctly contructed as is CString bus and the line

busNumberSQL[1] = bus;

works as expected. This can be seen by putting a breakpoint in at

return 0;

and seeing the variables in a Watch. Copy the expanded Watch details (Name, Value & Type) to an EXCEL sheet.
..................

Next, add the compiler switch /clr and rerun the code.

CString bus is constructed correctly BUT something weird happens in the construction of CString busNumberSQL[2].

Now,
busNumberSQL[1] = bus;

results in the address of bus as an integer being assigned to busNumberSQL[1], and look at the Watch details!!

Copy the expanded Watch details (Name, Value & Type) to an EXCEL sheet

Name: busNumberSQL; Value: {Length=2}; Type: ATL::CStringT<char,strtraitmfc<char,atl::chtraitscrt<char> > >[] ...(Note no dimension at end compared to the "no /clr" case.
Next Watch line: [0] 2083454756 __int32
Next Watch line: [1] 3103464 __int32

My conclusion is that busNumberSQL[2] is not an array of CString.

Of course, I need the /clr in order to use ADO.NET!

It seems as though a CString works, but a CString array for some (unknown) cannot even be defined.

Do you have any light for me? (I have not got into your previous post yet on Marshall)

Best regards

Doug.

(In case you are wondering I am very much a beginner with C++ and .NET)

Doug

Re: ADO.NET : SqlDataReader : I need to assign retrieved value to C++ variable

Doug15-Oct-02 12:17

Doug

15-Oct-02 12:17

Thanks Nish,

I have definitely got this working where the native C++ type is int and I am confident that I can now handle any numeric type.

What I am battling with is where the .NET value retrieved is a String (the SQL field is text).

I have managed to get the following to work:

String* busNumberSQL __gc[] = new String* __gc[97];
short halfhoursSQL = 0;
.
.
.
Console::WriteLine(myReader->GetString(0));
halfhoursSQL++;
busNumberSQL[halfhoursSQL] = Convert::ToString(myReader->GetValue(0));

However busNumberSQL is a managed array of type String*.

Now I need assign the value of busNumberSQL[halfhoursSQL] to a CString or native C++ string type. All I seem to end up with is the decimal representation of the hexidecimal memory address.

I have also tried:
Convert::ToChar(myReader->GetValue(0)) to assign one character
(Convert::ToString(myReader->GetValue(0)))->ToCharArray()

As I continue to try different things, do you have any idea how this may be done? I will let you know if I crack it.

(With the old ADO I was able to do this by doing a double cast: ---> _bstr_t --> LPCTSTR and then doing a simple assignment to a CString)

Thanks and regards

Doug

Doug

Re: ADO.NET : SqlDataReader : I need to assign retrieved value to C++ variable

Doug16-Oct-02 12:39

Doug

16-Oct-02 12:39

Hi Nish

Re: ADO.NET : SqlDataReader : I need to assign retrieved value to C++ variable

I have found the source of the problem expressed in the thread "ADO.NET : SqlDataReader : I need to assign retrieved value to C++ variable":
http://www.codeproject.com/script/comments/forums.asp?forumid=3785#xx309754xx

but do not yet know why it occurs or how I can fix it.

The problem arises with the /clr compiler setting.

Here is the code to illustrate this:

/////////////////////////////////////////////////////////

#include <stdafx.h>
#include <cstdlib>
#include "try_ADONET.h"

//#using <mscorlib.dll>
//#using <system.dll>
//#using <system.data.dll> // This is required for the ADO.NET Provider

using namespace std;
//using namespace System;

int Main()
{
CString busNumberSQL[2];
CString bus = "Hello";
busNumberSQL[1] = bus;

return 0;
}

////////////////////////////////////////////////////////

Without the /clr setting the array of CString busNumberSQL[2] is correctly contructed as is CString bus and the line

busNumberSQL[1] = bus;

works as expected. This can be seen by putting a breakpoint in at

return 0;

and seeing the variables in a Watch. Copy the expanded Watch details (Name, Value & Type) to an EXCEL sheet.
..................

Next, add the compiler switch /clr and rerun the code.

CString bus is constructed correctly BUT something weird happens in the construction of CString busNumberSQL[2].

Now,
busNumberSQL[1] = bus;

results in the address of bus as an integer being assigned to busNumberSQL[1], and look at the Watch details!!

Copy the expanded Watch details (Name, Value & Type) to an EXCEL sheet

Name: busNumberSQL; Value: {Length=2}; Type: ATL::CStringT<char,strtraitmfc<char,atl::chtraitscrt<char> > >[] ...(Note no dimension at end compared to the "no /clr" case.
Next Watch line: [0] 2083454756 __int32
Next Watch line: [1] 3103464 __int32

My conclusion is that busNumberSQL[2] is not an array of CString.

Of course, I need the /clr in order to use ADO.NET!

It seems as though a CString works, but a CString array for some (unknown) cannot even be defined.

Do you have any light for me? (I have not got into your previous post yet on Marshall)

Best regards

Doug.

(In case you are wondering I am very much a beginner with C++ and .NET)

Doug

Unmanaged Event

ajb10-Oct-02 11:41

ajb

10-Oct-02 11:41

I'm using a purchased unmanaged library that controls some hardware and throws a windows event (returning an event HANDLE)when the hardware is ready. I'd like to use this event to update my windows form. Is there any way to marshall the event HANDLE to a .NET event?

Including Wbemdisp?

EnkelIk9-Oct-02 2:48

EnkelIk

9-Oct-02 2:48

Hi.

I want to use WMI functions in a managed C++ project. I have found these functions and classes are defined in the wbemdisp.tlb, but I have not managed to include this library in my class.

In VB.NET I just had to add a reference to the library, so I ought to be possible in C++ as well, but how?

Best regards
/EnkelIk

Re: Including Wbemdisp?

Michael Mac11-Oct-02 2:20

Michael Mac

11-Oct-02 2:20

See System::Management namespace. It wraps WMI.
Smile | :)

43 68 65 65 72 73 2c
4d 69 63 68 61 65 6c

How do I make an assembly?

EnkelIk7-Oct-02 22:31

EnkelIk

7-Oct-02 22:31

Hi.

I have created an application starting with a "Managed C++ empty project". Now I would want the users to be able to run this project from a local server and therefore need their .NET frameworks to trust the application.

How do I make my project an assembly? I tried just adding an AssemblyInfo.cpp file to my project and generating a keyfile, but that did of course not do the trick. Using the Microsoft .NET framework wizard, it does not recognize the *.exe as an Assembly. What more do I need to do?

Regards
/EnkelIk

Re: How do I make an assembly?

EnkelIk9-Oct-02 21:56

EnkelIk

9-Oct-02 21:56

I just realized that even if I create a Managed C++ Application project and get the AssemblyInfo file automatically generated I still get the error "Unable to load assembly ....." when I try to set "Trust an assembly" in the .net wizards. If I try with a dll though everything works fine.

What am I doing wrong? The only thing I did after having created the Managed C++ application as well as the Managed C++ class library was to compile them. I've tried adding a strong name key but that did not help.

All help will, as always, be greatly appreciated.
/EnkelIk

how to?

imran_rafique5-Oct-02 15:27

imran_rafique

5-Oct-02 15:27

how to creat a setup project that will install an application through a wizerd ?
how to creat DNS programatically (driver name that we manually make in DB projects)?
how to logoff and login programatically ?

r00d0034@yahoo.com

Re: how to?

Slayer14-Oct-02 3:09

Slayer

14-Oct-02 3:09

There are some companies that provides such programs.But i don't know how and where they can be found.

Using STL in MC++

Anonymous2-Oct-02 9:09

Anonymous

2-Oct-02 9:09

Hi Guys,

How can I add STL lib in MC++?

Thanks

Re: Using STL in MC++

Alexandru Savescu14-Nov-02 5:42

Alexandru Savescu

14-Nov-02 5:42

You just include the header files and use it as if you were writing a standard C++ application. There's nothing special about it.

Best regards,
Alexandru Savescu

P.S. Interested in art? Visit this!

New line in textbox?

EnkelIk30-Sep-02 20:42

EnkelIk

30-Sep-02 20:42

Hi.

I'm using a TextBox to display status messages to the user (like:
"Retrieving MAC address: 002345235cbd"
"Retrieving IP-number: 10.10.10.10"
and so on). The messages are added line by line so that the first message is never over written. The only way I have found to be able to control when to get a new line is to use a String array and the set_Lines method, since neither \n, \v or \f has the desired effect. Is there no better way?

The main problem using the TextBox->set_Lines method is that all the lines are set at the same time so I can't have different fontstyle on different lines.

Anyone has a solution? Or should I use something else than TextBox to display the messages? If so what?

Regards
/EnkelIk

Re: New line in textbox?

Christian Graus30-Sep-02 22:55

Christian Graus

30-Sep-02 22:55

Environment.NewLine is the .NET friendly way to make something multiline, and make sure the text control is set to multiline also.

Christian

Hey, at least Logo had, at it's inception, a mechanical turtle. VB has always lacked even that... - Shog9 04-09-2002

During last 10 years, with invention of VB and similar programming environments, every ill-educated moron became able to develop software. - Alex E. - 12-Sept-2002

Re: New line in textbox?

group_captain_mandrake17-Oct-02 18:04

group_captain_mandrake

17-Oct-02 18:04

Yes, I can't find a better way than using strings and then doing something like:

String* break="\r\n";
String::Concat(textString1,break,textString2);

This is obviously a lousy solution because you have to put all of your strings together before you even display them!

MS says that we shouldn't even be using strings anymore if they have to be manipulated repeatedly, but should use stringBuilder instead. Unfortunately, stringBuilder has been proven in clinical trials to cause insanity in 3 out of 5 users.

how to?

imran_rafique29-Sep-02 16:36

imran_rafique

29-Sep-02 16:36

this line of code
IFormatter formatter = new BinaryFormatter();Stream stream = new FileStream("MyFile.bin", FileMode.Create, FileAccess.Write, FileShare.None);formatter.Serialize(stream, obj);stream.Close();

alwas write data at the end of file or not ?
i mean there are alot of Objects .
where it write in the file?

this line of code
object obj = formatter.Deserialize(stream);
alwas read data from the begining of file or not ?
i mean there are alot of Objects.
where it read from the file?

r00d0034@yahoo.com

HOW to creat FileStream?

imran_rafique28-Sep-02 15:31

imran_rafique

28-Sep-02 15:31

HOW to creat FileStream object that coud write into a file ?
can you explain any of its constructor?

how to write data using FileStream into a file or read theobject from a file to the FileStream object only then it is possible to serialize or Deserialize it?

i want to write a hastable object into a file that contain class objects,and class objects further contain hashtable and other class objects.
may i write that hashtable into a file and retrive again?

i study the api but could not understand what methods to use.

r00d0034@yahoo.com

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