Question

我从数据库中获取一些信息，我想在计算中使用它。但由于我写的东西，我无法将其转换为数字。我收到了System::Object^。这是代码的一部分：

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...");

我想将numberOfProducts用作数字。我的意思是键入double或integer。我怎样才能改变它？

Answer 1

只需使用safe_cast将Object^转换为适当的类型即可。本页详细介绍了这一点：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);

因为只能有一个底层类型（我不知道你的情况是什么），只有其中一个可以工作 - 另一个会抛出异常。重点是，您的第一步是确定实际的基础类型（可能是double，float或int）。

System :: Object在C ++ / CLI中为int或double

1 个答案: