Bison for C++

[魏佳]

Hello Every one,

I have a problem with bison, please help me.

How do I add "friend class CSV" to c++ parser file that was maked by bison?
for example

csv_parser.ypp

...
%define parser_class_name "csv_parser"
...

I want get

class csv_parser
{
...
public:
    friend class CSV;
...
};

Best Wishes
Thank you!!!