Regex to match a C-style multiline comment
Solution 1:
The best multiline comment regex is an unrolled version of (?s)/\*.*?\*/ that looks like
String pat = "/\\*[^*]*\\*+(?:[^/*][^*]*\\*+)*/";
See the regex demo and explanation at regex101.com.
In short,
-
/\*- match the comment start/* -
[^*]*\*+- match 0+ characters other than*followed with 1+ literal* -
(?:[^/*][^*]*\*+)*- 0+ sequences of:-
[^/*][^*]*\*+- not a/or*(matched with[^/*]) followed with 0+ non-asterisk characters ([^*]*) followed with 1+ asterisks (\*+)
-
-
/- closing/
David's regex needs 26 steps to find the match in my example string, and my regex needs just 12 steps. With huge inputs, David's regex is likely to fail with a stack overflow issue or something similar because the .*? lazy dot matching is inefficient due to lazy pattern expansion at each location the regex engine performs, while my pattern matches linear chunks of text in one go.
Solution 2:
Try using this regex (Single line comments only):
String src ="How are things today /* this is comment */ and is your code /* this is another comment */ working?";
String result=src.replaceAll("/\\*.*?\\*/","");//single line comments
System.out.println(result);
REGEX explained:
Match the character "/" literally
Match the character "*" literally
"." Match any single character
"*?" Between zero and unlimited times, as few times as possible, expanding as needed (lazy)
Match the character "*" literally
Match the character "/" literally
Alternatively here is regex for single and multi-line comments by adding (?s):
//note the added \n which wont work with previous regex
String src ="How are things today /* this\n is comment */ and is your code /* this is another comment */ working?";
String result=src.replaceAll("(?s)/\\*.*?\\*/","");
System.out.println(result);
Reference:
- https://www.regular-expressions.info/examplesprogrammer.html
Solution 3:
Try this one:
(//[^\n]*$|/(?!\\)\*[\s\S]*?\*(?!\\)/)
If you want to exclude the parts enclused in " " then use:
(\"[^\"]*\"(?!\\))|(//[^\n]*$|/(?!\\)\*[\s\S]*?\*(?!\\)/)
the first capturing group identifies all " " parts and second capturing group gives you comments (both single line and multi line)
copy the regular expression to regex101 if you want explanation