Re: [Boost-users] Problems matching parantheses in a string using boost::regex 1.42.0 on a amd64 debian system

Subject: Re: [Boost-users] Problems matching parantheses in a string using boost::regex 1.42.0 on a amd64 debian system
From: Simon Hoerder (simon_at_[hidden])
Date: 2011-08-22 13:28:58

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On 22/08/11 18:11, Bill Buklis wrote:
> On 8/22/2011 11:56 AM, Simon Hoerder wrote:
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>>
>> Hi,
>>
>> I'm fairly new to boost libraries but searched the documentation and
>> googled for an answer to my problem but couldn't come up with something.
>> Please bear with me.
>>
>> I am using boost::regex (version 1.42.0 on debian amd64 machine) to
>> parse a vhdl-like file. To this end, I am trying to use the regular
>> expression
>> boost::regex("^SIGNAL ([A-Z0-9_]*?): STD_LOGIC_VECTOR\( ([0-9]*?) DOWNTO
>> ([0-9]*?)\);$");
>> to match strings like:
>> SIGNAL W07: STD_LOGIC_VECTOR( 255 DOWNTO 0);
>>
>> My problem is that matching those parantheses in the string doesn't work
>> - - I've tested the regexp under perl and it works fine but boost::regexp
>> and C++ works only if I remove the brackets from the string and from the
>> regular expression.
>>
>> Issues I observed&  tested:
>> 1) '\(' ... '\)' no match but g++ complains about an unknown escape
>>     sequence '\)'.
>> 1a) Using '\(' ... ')' doesn't match. (I would have expected an
>>      exception to be thrown but none whatsoever.)
>> 2) '0x28' ... '0x29' doesn't match. (0x28 = ASCII '(', 0x29 = ASCII ')')
>> 3) '\Q(\E' ... '\Q)\E' no match but g++ complains about an unknown
>>     escape sequence '\Q'.
>> 4) If I try to match only one of the brackets and remove the other from
>>     the string&  regex I get one of the following:
>>     '\(' ... gives me:
>> terminate called after throwing an instance of
>> 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::regex_error>
>>
>>> '
>>    what():  Found a closing ) with no corresponding openening
>> parenthesis.  The error occured while parsing the regular expression
>> fragment: '?([0-9]*?)>>>HERE>>>);$'.
>>     ... '\)' gives me:
>> terminate called after throwing an instance of
>> 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::regex_error>
>>
>>> '
>>    what():  Unmatched marking parenthesis ( or \(.  The error occured
>> while parsing the regular expression fragment: '[0-9]*?);$>>>HERE>>>'.
>> 5) Even
>>     boost::regex("^SIGNAL W07: STD_LOGIC_VECTOR\( 255 DOWNTO 0\);$");
>>     fails to match
>>     SIGNAL W07: STD_LOGIC_VECTOR( 255 DOWNTO 0);
>>
>> Points 1a and 4 suggests that boost::regex treats even escaped
>> parantheses as special characters which is quite surprising to me. I am
>> sure a lot of people successfully used boost::regex to match parantheses
>> so I do wonder which part of the documentation I have missed.
>>
>> I'd be happy to provide more debugging information if you tell me how to
>> produce it.
>>
>> Many thanks,
>> Simon Hoerder
>>
> 
> You need to escape the slash character for normal C++ processing, i.e.
> double slash.
> It should be "\\(" and "\\)" to catch a parentheses.
> 

Works now, thanks. :-)

Cheers, Simon

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