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

From: Olaf Peter (ope-devel_at_[hidden])
Date: 2008-08-14 01:47:25

>> 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?

one newline; the "Hello" string is '\0' terminated. As next a function 
call with "\n" is performed, than a "World\0" string followed by a "\n" 
on next member function call.

Note, my member function expect a const std::string& as argument.

>> 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?

The indicator for this is the member function call with "\n". python's 
output wants a line break and I have to set a prefix prompt on each 
line. The same with python's "\n" terminated strings I got.

>> 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'"?

a single means here a function call with "\n" only, terminated means a 
string with trailing "\n", e.g. the "Traceback ...\n" string.

>> 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.

this warnings comes from VS2005 only - I assume that are the 64bit 
compatibility check or something special. On linux's gcc 3.4 no warnings 
-  even with "-Wall".

The problem ask here is a down break of my postings to sig-c++ 
(http://www.nabble.com/-boost.python--general-questions-td18950884.html) 
even with regular expression instead boost::tokeniterator. At this time 
I have more information on how the strings comes from redirected python 
output ( I did run it inside the debugger ;-) My assumption on this 
posting about the internal name lookup where wrong.

Thanks,
Olaf