private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) {
Stream^ myStream;
    openFileDialog1->Filter = "Текстовые файлы (*.txt)|*.txt|Все файлы (*.*)|*.*";

    if (openFileDialog1->ShowDialog() == System::Windows::Forms::DialogResult::OK)
    {
        label1->Text = openFileDialog1->FileName;
         if ( (myStream = openFileDialog1->OpenFile()) != nullptr )
     {
        // Insert code to read the stream here.
        myStream->Close();
           textbox1->text=Convert::ToString(myStream);

     }

    }

}

textBox1->Text = System::IO::File::ReadAllText(openFileDialog1->FileName);