get directory from file path c++

The initialisation is incorrect as you need to escape the backslashes:

string filename = "C:\\MyDirectory\\MyFile.bat";

To extract the directory if present:

string directory;
const size_t last_slash_idx = filename.rfind('\\');
if (std::string::npos != last_slash_idx)
{
    directory = filename.substr(0, last_slash_idx);
}