Re: [Boost-users] regular expression help

From: John Maddock (john_at_[hidden])
Date: 2006-07-28 05:08:35

llwaeva_at_[hidden] wrote:
> Here, expK found all the substring matching %K{xxx} (not including
> double % case). But the program didn't give
> me what I want, I guess the problem is from the expression where {
> and } is not expressed correctly. However, I
> didn't  found how to express { and } in the document. Here is my
> guess of the correct form, tell me if it is
> correct or not
>
> 1) boost::regex expK("[^%]*%K\{([^\r\n])\}");   // here \{ represents
> { and \} represents } 2) boost::regex
> expK("[^%]*%K[{]{1}([^\r\n])[}]{1}");   // use [{]{1} and [}]{1} to
> limit the { and } occur once exactly 3) boost::regex
> expK("[^%]*%K\\{([^\r\n])\\}");   // here \\{ represents { and \\}
> represents }
>
> which one is correct? or all is wrong?

{ and } are repetition operators in regexes, if you want to match a literal 
{ or } you can use either [{] or \{, the latter when embedded in a C++ 
string becomes "\\{" since the compiler processes the first \ before the 
regex engine gets to see it.

John.