Call by Reference problem

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I am trying to get connection string and provider name using a function like this:

C#

MyDriver* GetDSNAndProvider(const String* sName,String *sDSN,String *sProvider)
{
    if(1)
    {
        sDSN="Data Source=(local);Initial Catalog=labops;User Id=labops;      Password=99w1ldf1re;";
        sProvider="System.Data.SqlClient";
        MyDriver *myIface = new SQlClientDriver();
       return myIface;
    }
    else
    {
        return NULL;
    }
}

and this is my Main()

C#

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

	String *sDQN,*sProvider;
	try
    {
	MyDriver *MDriverIface=GetDSNAndProvider("sqlServer",sDQN,sProvider);
        Console::Write(String::Concat("Provider Name ",   sProvider));
    }
}

I am getting the provider name as null, How we can do this call by reference in c++.net. I am compiling this code using "Common Language Runtime Support, Old Syntax (/clr:oldSyntax)".

Posted 25-Nov-14 3:07am

Member 11168418

Updated 25-Nov-14 17:54pm

v5

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Comments

Tomas Takac 25-Nov-14 9:17am

Your method expects provider name "sql server" but you are passing it as "sqlServer".

Member 11168418 25-Nov-14 23:37pm

I have tried with if condition true at all time, replaced with if(1){}, still return nothing.

Member 11168418 25-Nov-14 23:41pm

I tried like this also:
if(1)
{
sDSN="Data Source=(local);Initial Catalog=labops;User Id=labops;Password=99w1ldf1re;";
sProvider="System.Data.SqlClient";
MyDriver *myIface = new SQlClientDriver();
return myIface;

}
else
{
return NULL;
}
still not working.

2 solutions

Solution 1

why dont you check and handle that case:

C#

if( sProvider == null)
{
  sProvider = "my fallback";
}

And as Tomas wrote: Your method expects provider name "sql server" but you are passing it as "sqlServer".!!! :-O

Posted 25-Nov-14 3:29am

KarstenK

Comments

Member 11168418 25-Nov-14 23:40pm

i just tried without those conditions like
if(1)
{
sDSN="Data Source=(local);Initial Catalog=labops;User Id=labops;Password=99w1ldf1re;";
sProvider="System.Data.SqlClient";
MyDriver *myIface = new SQlClientDriver();
return myIface;

}
else
{
return NULL;
}

inside GetDSNAndProvider() function, still return nothing.

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bling · Accepted Answer · 2014-11-25T08:14:00

This looks like C++/CLI.

1. Your gc objects need hats eg. "^".
2. you're passing pointer values which are not the same as references.
3. you fail to return the new pointer to the oracle interface.

I created a mock of the two MyDriver implementations to verify it works. I'm assuming a C++ class and not a ref class. I noticed the typo in the SQL server name.

C++

#include "stdafx.h"
#include <stddef.h>
#include <string.h>

using namespace System;

struct MyDriver
{
	int common;
public:
	virtual const char *whoami() const = 0;
};

struct SQlClientDriver : MyDriver
{
	int sql;
public:
	const char *whoami() const { return "SQL"; }
};

struct OracleClientDriver : MyDriver
{
	int oracle;
public:
	const char *whoami() const { return "Oracle"; }
};

MyDriver* GetDSNAndProvider(String^ sName, String ^ &sDSN, String ^ &sProvider)
{
    if(sName == "sqlServer")
    {
		sDSN="Data Source=(local);Initial Catalog=myDb;User Id=user;Password=pw;";
		sProvider="System.Data.SqlClient";
		return new SQlClientDriver();//class is defined there
	}
	else if (sName == "Oracle")
	{
		sDSN="Data Source=(local);Initial Catalog=myOracleDB;User Id=user;Password=pw;";
		sProvider="System.Data.SqlClient";
		return new OracleClientDriver();//class is defined there
	}
	return NULL;
}

int main(array<system::string xmlns:system="#unknown"> ^args)
{
    Console::WriteLine(L"Starting ...");
    String^ sDQN, ^sProvider;

    MyDriver *MDriverIface = GetDSNAndProvider("sqlServer",sDQN,sProvider);
    Console::WriteLine("Provider Name {0}", sProvider);
    if (MDriverIface != NULL)
    {
        const char *whoami = MDriverIface->whoami();
        IntPtr pass = (IntPtr)const_cast<char>(whoami);
        String^ marshal = System::Runtime::InteropServices::Marshal::PtrToStringAnsi(pass, strlen(whoami));
        Console::WriteLine(marshal);
    }

    Console::WriteLine(L"Done.");
    Console::ReadLine();
    return 0;
}
</char></system::string></string.h></stddef.h>

I purposely omitted the try/catch to make errors more obvious.