Managed C++/CLI

Problem connecting with OleDbConnection & C++

12-Dec-06 15:30

OK, then you need to ask in the right forum. 'managed' means this forum is for .NET C++ questions.

Christian Graus - Microsoft MVP - C++
Metal Musings - Rex and my new metal blog

bamagrad7-Dec-06 16:48

bamagrad

7-Dec-06 16:48

Hi
Could someone point out my code error here.

When I try to compile I get a C2065 OleDbConnection undeclared identifier
error
msg.

Here is my code:

#using <mscorlib.dll>

#using <system.data.dll>
using namespace System;
using namespace System::Data;
using namespace System::Data::OleDb;

#include "stdafx.h"

int _tmain(int argc, _TCHAR* argv[])
{

// The connection
//string cnNwind;

OleDbConnection * conn = new OleDbConnection();

conn->ConnectionString = S "Provider=Microsoft.Jet.OLEBD.4.0; "
S"Data Source=C:\my_databases\taxLots.mdb";

// The connection string

try
{
// Open Database
conn->Open();
Console::WriteLine(S"Connected to database successfully!");
}
catch (OleDbException * pe)
{
Console::Write(S"Error occurred: ");
Console::WriteLine(pe->Message);
}

// Close Connection
if (conn->State != ConnectionState::Closed)
{
conn->Close();
}
Console::WriteLine(S"The database connection is now closed");

return 0;
}

Thanks for any insights.

--
BamaGrad

Re: Problem connecting with OleDbConnection & C++

bamagrad8-Dec-06 7:30

bamagrad

8-Dec-06 7:30

Hi;

I finally figured out my problem.

You have to have two references in order for your declared object to
recognized.

Add them to your references folder in the solutions explorer.

They are:

System
System.Data

Howto Return vector from a function

TurboNext7-Dec-06 7:27

TurboNext

7-Dec-06 7:27

Hi All,

I have a vector defined of type vector<char> theString in a function. I need to return this string to the main program, what should be the return type of the function?. I am using "char *" and I have a problem with it. Please let me know what should be the return type and how the function declaration should be. Any help greatly appreciated.

Thanks,
Turbo

char * readline(SOCKET *theSocket)
{
vector<char> theString;
char buffer;
bool bStringEnding = true;

while(bStringEnding)
{
if (recv(*(theSocket), &buffer, 1, 0) == -1)
{
return SERVER_SOCKET_ERROR;
WSACleanup();
}

if(buffer == '\n')
{
bStringEnding = false;
return theString;

}
else
theString.push_back(buffer);

}
return theString;
}

Christian Graus7-Dec-06 9:19

7-Dec-06 9:19

This is not managed C++, therefore you're asking in the wrong forum.

Why do you need vector<char> ? What's wrong with std::string ?

Christian Graus - Microsoft MVP - C++
Metal Musings - Rex and my new metal blog

led mike7-Dec-06 12:50

led mike

7-Dec-06 12:50

TurboNext wrote:
if (recv(*(theSocket), &buffer, 1, 0) == -1)

Not very efficient way to perform socket communications. Sigh | :sigh:

led mike

lafleon8-Dec-06 13:48

lafleon

8-Dec-06 13:48

Just try

1. vector<char> readline(SOCKET *theSocket); or
2. bool readline(SOCKET *theSocket, vector<char>* pVevChr);

Regards

Context sensitive keywords and mixed mode programming

lafleon8-Dec-06 13:51

lafleon

8-Dec-06 13:51

Just try

1. vector < char > readline(SOCKET *theSocket); or
2. bool readline(SOCKET *theSocket, vector < char > * pVevChr);

Regards

User 5838526-Dec-06 13:47

User 583852

6-Dec-06 13:47

We have been using the new override keyword in standard c++ projects.
I have a standard c++ library that includes something like this

class Base
{
virtual bool DoSomething() = 0;
};

class Derived
{
bool DoSomething() override;
};

This compiles fine

This header is included in my managed c++/cli project and because the override keyword has a slightly differnt meaning in CLI I get the following error when compiling the CLI project that includes this file

error C2217: 'override' requires 'virtual'

The simple solution is to change the derived class to be like this

class Derived
{
virtual bool DoSomething() override;
};

Obviously the preprocessor is doing all the includes before the compiler sees this so it has no way of knowing that the code come from a standard c++ project. Is there any other way to resolve this without changing the function declaration?

System.IO.Path.IsPathRooted() does not behave as I would expect

Re: Context sensitive keywords and mixed mode programming

George L. Jackson6-Dec-06 14:43

George L. Jackson

6-Dec-06 14:43

Try surrounding the code with the managed/unmanaged pragmas.

Re: Context sensitive keywords and mixed mode programming

George L. Jackson6-Dec-06 14:51

George L. Jackson

6-Dec-06 14:51

Josh,

The native code also needs override paired with virtual also! Here is an example taken out of Microsoft's documentation (How to: Declare Override Specifiers in Native Compilations ):

// override_native_keyword.cpp
#include <stdio.h>
__interface I1 {
   virtual void f();
};

class X : public I1 {
public:
   virtual void f() override {}   // OK
   virtual void g() override {}   // C3668 I1::g does not exist
};

Re: Context sensitive keywords and mixed mode programming

User 5838526-Dec-06 14:57

User 583852

6-Dec-06 14:57

George L. Jackson wrote:
The native code also needs override paired with virtual also! Here is an example taken out of Microsofts documentation:

That is what I thought. The code in question was written by someone else and committed to source control yesterday. It does appear to compile and run without the virtual keyword. I think Ill have a word with him.

Interestingly the prama does not resolve the issue which would suggest that the /CLI option makes the compiler produce this error.

Thanks again for your help

System.IO.Path.IsPathRooted() does not behave as I would expect

Re: Context sensitive keywords and mixed mode programming [modified]

George L. Jackson6-Dec-06 15:28

George L. Jackson

6-Dec-06 15:28

Well, it does compile natively just with the "override" key word. Intellisense recognizes the method as "virtual" also. I guess Microsoft is just using "override" more for documentation/information purposes!

Anyway, I also found this: http://blogs.msdn.com/doronh/archive/2006/10/27/the-override-keyword-can-be-used-in-c-afterall.aspx[^]

George

-- modified at 20:41 Wednesday 6th December, 2006

Re: Context sensitive keywords and mixed mode programming

User 5838526-Dec-06 17:37

User 583852

6-Dec-06 17:37

Thanks again for all your help mate

We use the override keyword in our nonmanaged code to catch cases where people override a method thats not virtual

System.IO.Path.IsPathRooted() does not behave as I would expect

Copying data from unmanaged to managed

kristmun6-Dec-06 4:48

kristmun

6-Dec-06 4:48

Hi,
I am trying to copy data from a structure

<br />
typedef struct OctetString {<br />
    unsigned int   length;<br />
    unsigned char  *value;<br />
} OctetString;<br />

I have only managed to copy the value using a for-loop and an ArrayList

<br />
OctetString* data;<br />
ArrayList^ bits = gcnew ArrayList();<br />
for(unsigned int i=0;i<data->length;i++)<br />
{<br />
  bits->Add((char)*data->value);<br />
  data->value++;<br />
}<br />

My question is: Is there a better way to copy the data into the ArrayList, and is
there a more suitable structure than a ArryList to handle binary data of different lengths?

/krissi

Re: Copying data from unmanaged to managed

Nish Nishant6-Dec-06 5:58

Nish Nishant

6-Dec-06 5:58

You could use an equivalent value class :-

value class MOctetString
{
   unsigned int length;
   array<unsigned char>^ value;
};

Regards,
Nish

Nish’s thoughts on MFC, C++/CLI and .NET (my blog)
Currently working on C++/CLI in Action for Manning Publications. (*Sample chapter available online*)

Re: Copying data from unmanaged to managed

led mike6-Dec-06 7:29

led mike

6-Dec-06 7:29

kristmun wrote:
Is there a better way to copy the data into the ArrayList, and is
there a more suitable structure than a ArryList to handle binary data of different lengths?

They hide that information in the documentation[^]

led mike

Re: Copying data from unmanaged to managed

kristmun8-Dec-06 5:51

kristmun

8-Dec-06 5:51

Hi guys,
thanks for the advice.
It works now using the Copy method

<br />
array<unsigned char>^ value = {'a','b','c'};<br />
char* ptr = new char[value->Length];<br />
Marshal::Copy(value,0,(IntPtr)ptr,value->Length);<br />

and the other way around

<br />
int length = 3;<br />
char str[] =  {'d','e','f'};<br />
char* pStr = &str[0];<br />
array<unsigned char>^ strArr = gcnew array<unsigned char>(length);<br />
Marshal::Copy((IntPtr)pStr,strArr,0,length);<br />

I didn't quite get the value class way Sigh | :sigh:

std not recognized

Anil_vvs6-Dec-06 0:12

Anil_vvs

6-Dec-06 0:12

Hi All,

My application doesnt compile if I use anything from namespace std. I have tried "using namespace std" and std::

Can anyone tell me what the problem could be?

Extremely sorry for asking a basic question. I am just a starter. Hope you all understand. Smile | :)

Thanks and Regards,
Anil

Christian Graus6-Dec-06 0:23

6-Dec-06 0:23

When you say it doesn't compile, what is the error ?

Did you #include what you're trying to use ?

Christian Graus - Microsoft MVP - C++
Metal Musings - Rex and my new metal blog

Anil_vvs6-Dec-06 0:56

Anil_vvs

6-Dec-06 0:56

Hi Christian,

Now the previous error disappeared. But I still get

error C2079: 'Logger::m_oStream' uses undefined class 'std::basic_ofstream<_Elem,_Traits>'
with
[
_Elem=char,
_Traits=std::char_traits<char>
]

Can you please help? I am using Visual Studio .Net 2003

Thanks and Regards,
Anil

Nish Nishant6-Dec-06 6:00

Nish Nishant

6-Dec-06 6:00

If you could post a minimal code snippet that reproduces the error, it'd be easier to figure otu what headers you are missing.

Regards,
Nish

Nish’s thoughts on MFC, C++/CLI and .NET (my blog)
Currently working on C++/CLI in Action for Manning Publications. (*Sample chapter available online*)

Christian Graus6-Dec-06 9:34

6-Dec-06 9:34

Are you including iostream ( not iostream.h ) ?

Christian Graus - Microsoft MVP - C++
Metal Musings - Rex and my new metal blog