Re: [Boost-users] [boost.xpressive] RE for replacing problem

From: Eric Niebler (eric_at_[hidden])
Date: 2008-08-13 18:14:55

Olaf Peter wrote:
> Hi,
> 
> my member function write() get called with string arguments like:
> 
> Hello
> \n
> World
> \n
> Traceback ...\n
> NameError
> :
>  name ... not defined
> \n

I'm a little confused. Is there a newline after "Hello", or two?

> etc.
> 
> I want to add a prefix (a prompt '>>>' concete) so that the result will 
> become:
> 
>  >>> Hello
>  >>> World
>  >>> Traceback ....
>  >>> NameError: name ... not defined

And how do you know to put "NameError", ":", and "name ... not defined" 
all on one line, but "Hello" and "World" on different lines?

> Yes, this comes from redirected python output.
> 
> The simplest solution seems to use regex/xpressive:
> 
>     class redirector
>     {
>         const std::string m_prompt;
>         const xpr::sregex m_re;
>         const std::string m_re_fmt;
> 
>     public:
>         redirector(const std::string& prompt = ">>> ")
>             : m_prompt(prompt),
>               m_re(xpr::sregex::compile("(\\n)!")),
>               m_re_fmt(m_prompt + "\n")
>         { }
> 
>         void write(const std::string& text) {
> 
>             std::cout << m_prompt
>                       << xpr::regex_replace(text, m_re, m_re_fmt);
>         }
>     ...
>     };
> 
> where my regex won't work. What is the correct one since I can get a 
> single '\n', a terminated '\n' 

What is a "terminated '\n'"?

> or multiline strings separated by '\n'. 
> Is this approach good for this problem?

A regex is probably your best bet. If you define the problem better, I 
or someone else here can probably help. Or, there are plenty of online 
resources that could help you author the regex. Check out the Regex 
Coach: http://www.weitz.de/regex-coach/

> Anyway, I get a lot of warnings from constructor and write function, any 
> ideas why?

You would need to provide a complete, compilable example and the 
compiler output, as well as giving me a clue what compiler you're using.

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com