Checking if a file opened successfully with ifstream

You can simply do this:

int devices::open_file(std::string _file_name)
{
    ifstream input_stream;    
    input_stream.open(_file_name.c_str(), ios::in);
    if(!input_stream)
    {
        return -1;
    } 
    file_name = _file_name;
    return 0;
}

fail() is not a static method, you must call it on an instance not a type, so if you want to use fail(), replace !input_stream with input_stream.fail() in my code above.

I do have to wonder what you’re trying to achieve here. You’re opening the file and immediately close it again. Are you simply trying to check if the file exists?