Regex skip in C++

Question

This is my string:

/*
  Block1 {

    anythinghere
  }
*/

// Block2 { }
# Block3 { }

Block4 {

    anything here
}

I am using this regex to get each block name and inside content.

regex e(R"~((\w+)\s+\{([^}]+)\})~", std::regex::optimize);

But this regex gets all inside of description too. There is a “skip” option in PHP that you can use to skip all descriptions.

What_I_want_to_avoid(*SKIP)(*FAIL)|What_I_want_to_match

But this is C++ and I cannot use this skip method. What should I do to skip all descriptions and just get Block4 in C++ regex?

This regex detects Block1, Block2, Block3 and Block4 but I want to skip Block1, Block2, Block3 and just get Block4 (skip descriptions). How do I have to edit my regex to get just Block4 (everything outside the descriptions)?

user557597 · Accepted Answer

Since you requested this long regex, here it is.

This will not handle nested Blocks like block{ block{ } }
it would match block{ block{ } } only.

Since you specified you are using C++11 as the engine, I didn't use
recursion. This is easily changed to use recursion say if you were to use
PCRE or Perl, or even BOOST::Regex. Let me know if you'd want to see that.

As it is it's flawed, but works for your sample.
Another thing it won't do is parse Preprocessor Directives '#...' because
I forgot the rules for that (thought I did it recently, but can't find a record).

To use it, sit in a while ( regex_search() ) loop looking for a match on
capture group 1, if (m[1].success) etc.. That will be your block.
The rest of the matches are for comments, quotes, or non-comments, unrelated
to the block. These have to be matched to progress the match position.

The code is long and redundant because there is no function calls (recursion) in the C++11 EMCAscript. Like I said, use boost::regex or something.

Benchmark

Sample:

/*
  Block1 {

    anythinghere
  }
*/

// Block2 { }

Block4 {

   // CommentedBlock{ asdfasdf }
    anyth"}"ing here
}

Block5 {

   /* CommentedBlock{ asdfasdf }
    anyth}"ing here
   */
}

Results:

Regex1:   (?:/\*[^*]*\*+(?:[^/*][^*]*\*+)*/|//(?:[^\]|\\n?)*?\n)|(?:"[^"\]*(?:$$\S\s][^"$$*)*"|'[^'\]*(?:$$\S\s][^'$$*)*'|(\w+\s*\{(?:(?:/\*[^*]*\*+(?:[^/*][^*]*\*+)*/|//(?:[^\]|\\n?)*?\n)|(?:"[^"\]*(?:$$\S\s][^"$$*)*"|'[^'\]*(?:$$\S\s][^'$$*)*'|(?!\})[\S\s][^}/"'\]*))*\})|[\S\s](?:(?!\w+\s*\{(?:(?:/\*[^*]*\*+(?:[^/*][^*]*\*+)*/|//(?:[^\]|\\n?)*?\n)|(?:"[^"\]*(?:$$\S\s][^"$$*)*"|'[^'\]*(?:$$\S\s][^'$$*)*'|(?!\})[\S\s][^}/"'\]*))*\})[^/"'\])*)
Options:  < none >
Completed iterations:   50  /  50     ( x 1000 )
Matches found per iteration:   8
Elapsed Time:    1.95 s,   1947.26 ms,   1947261 µs

Regex Explained:

    # Raw:        (?:/\*[^*]*\*+(?:[^/*][^*]*\*+)*/|//(?:[^\]|\\n?)*?\n)|(?:"[^"\]*(?:$$\S\s][^"$$*)*"|'[^'\]*(?:$$\S\s][^'$$*)*'|(\w+\s*\{(?:(?:/\*[^*]*\*+(?:[^/*][^*]*\*+)*/|//(?:[^\]|\\n?)*?\n)|(?:"[^"\]*(?:$$\S\s][^"$$*)*"|'[^'\]*(?:$$\S\s][^'$$*)*'|(?!\})[\S\s][^}/"'\]*))*\})|[\S\s](?:(?!\w+\s*\{(?:(?:/\*[^*]*\*+(?:[^/*][^*]*\*+)*/|//(?:[^\]|\\n?)*?\n)|(?:"[^"\]*(?:$$\S\s][^"$$*)*"|'[^'\]*(?:$$\S\s][^'$$*)*'|(?!\})[\S\s][^}/"'\]*))*\})[^/"'\])*)
    # Stringed:  "(?:/\*[^*]*\*+(?:[^/*][^*]*\*+)*/|//(?:[^\\]|\\\n?)*?\n)|(?:"[^"\\]*(?:\$$\S\s][^"\$$*)*"|'[^'\\]*(?:\$$\S\s][^'\$$*)*'|(\w+\s*\{(?:(?:/\*[^*]*\*+(?:[^/*][^*]*\*+)*/|//(?:[^\\]|\\\n?)*?\n)|(?:"[^"\\]*(?:\$$\S\s][^"\$$*)*"|'[^'\\]*(?:\$$\S\s][^'\$$*)*'|(?!\})[\S\s][^}/"'\\]*))*\})|[\S\s](?:(?!\w+\s*\{(?:(?:/\*[^*]*\*+(?:[^/*][^*]*\*+)*/|//(?:[^\\]|\\\n?)*?\n)|(?:"[^"\\]*(?:\$$\S\s][^"\$$*)*"|'[^'\\]*(?:\$$\S\s][^'\$$*)*'|(?!\})[\S\s][^}/"'\\]*))*\})[^/"'\\])*)"     


    (?:                              # Comments 
         /\*                              # Start /* .. */ comment
         [^*]* \*+
         (?: [^/*] [^*]* \*+ )*
         /                                # End /* .. */ comment
      |  
         //                               # Start // comment
         (?: [^\] | \ \n? )*?           # Possible line-continuation
         \n                               # End // comment
    )
 |                                 # OR,

    (?:                              # Non - comments 
         "
         [^"\]*                          # Double quoted text
         (?: \ [\S\s] [^"\]* )*
         "
      |  '
         [^'\]*                          # Single quoted text
         (?: \ [\S\s] [^'\]* )*
         ' 
      |  
         (                                # (1 start), BLOCK
              \w+ \s* \{               
              ####################
              (?:                              # ------------------------
                   (?:                              # Comments  inside a block
                        /\*                             
                        [^*]* \*+
                        (?: [^/*] [^*]* \*+ )*
                        /                                
                     |  
                        //                               
                        (?: [^\] | \ \n? )*?
                        \n                               
                   )
                |  
                   (?:                              # Non - comments inside a block
                        "
                        [^"\]*                          
                        (?: \ [\S\s] [^"\]* )*
                        "
                     |  '
                        [^'\]*                          
                        (?: \ [\S\s] [^'\]* )*
                        ' 
                     |  
                        (?! \} )
                        [\S\s]                          
                        [^}/"'\]*                      
                   )
              )*                               # ------------------------
              #####################          
              \}                               
         )                                # (1 end), BLOCK

      |                                 # OR,

         [\S\s]                           # Any other char
         (?:                              # -------------------------
              (?!                              # ASSERT: Here, cannot be a BLOCK{ }
                   \w+ \s* \{                      
                   (?:                              # ==============================
                        (?:                              # Comments inside a block
                             /\*                              
                             [^*]* \*+
                             (?: [^/*] [^*]* \*+ )*
                             /                                
                          |  
                             //                               
                             (?: [^\] | \ \n? )*?
                             \n                               
                        )
                     |  
                        (?:                              # Non - comments inside a block
                             "
                             [^"\]*                          
                             (?: \ [\S\s] [^"\]* )*
                             "
                          |  
                             '
                             [^'\]*                          
                             (?: \ [\S\s] [^'\]* )*
                             ' 
                          |  
                             (?! \} )
                             [\S\s]                          
                             [^}/"'\]*                       
                        )
                   )*                               # ==============================
                   \}                               
              )                                # ASSERT End

              [^/"'\]                         # Char which doesn't start a comment, string, escape,
                                               # or line continuation (escape + newline)
         )*                               # -------------------------
    )                                # Done Non - comments

Regex skip in C++

Answers (2)

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