Question

I’m taking some information from data base and i want to use it in calculations. But due to what i’written, i’m not able to convert it to number. I recieve System::Object^. here is the part of code:

OleDbConnection ^ cnNwind = gcnew OleDbConnection();

cnNwind-> ConnectionString = 
L"Provider = Microsoft.Jet.OLEDB.4.0;" 
L"Data Source = C:\\temp\\A.mdb";

try
{
    // Open the database
    cnNwind->Open();
    Console::WriteLine(L"Connected to database successfully!");

    // Count the customers
    OleDbCommand ^ cmProducts = gcnew OleDbCommand();
    cmProducts->CommandText = L"SELECT ID FROM Table1";
    cmProducts->CommandType = CommandType::Text;
    cmProducts->Connection = cnNwind;

    // Print the result
    Object ^ numberOfProducts = cmProducts->ExecuteScalar();
    Console::Write(L"Number of products: ");
    Console::WriteLine(numberOfProducts);
}
catch (OleDbException ^ pe)
{
    Console::Write(L"Error occurred: ");
    Console::WriteLine(pe->Message);
}
// Close the connection
if (cnNwind->State != ConnectionState::Closed)
{
    cnNwind->Close();
}

Console::WriteLine(L"The database connection is closed...");

I want to use numberOfProducts as a digit. I mean type double or integer. How can i transform it?

Answer 1

Simply use safe_cast to cast the Object^ to the appropriate type. This is covered in detail on this page: How to: Use safe_cast in C++/CLI

Object^ numberOfProductsObj = cmProducts->ExecuteScalar();
// IIF the underlying type is System::Int32
int numberOfProducts = safe_cast<int>(numberOfProductsObj);
// or, IIF the underlying type is System::Double
double numberOfProducts = safe_cast<double>(numberOfProductsObj);

Since there can only be one underlying type (and I don’t know what it is in your case), only one of these will work — the other will throw an exception. Point being, your first step is to determine the actual underlying type (presumably double, float, or int).