Regular Expression with (too?) many cases

I'm struggling with a Regex since a few hours and don't seem to find the last bit of the solution. I'm basically parsing a C-Header files line-by-line to find variables.

Following the possible cases of lines I may encounter which need to pass the Regex:

//#define variable_name { 300 }

#define variable_name { 300 }

//#define variable_name

#define variable_name

//#define variable_name { 300 } // Comment

#define variable_name { 300 } // Comment

#define variable_name // Comment

//#define variable_name // Comment

The following rules apply to each line above:

• A line can start optionally with commenting slashes (i.e. //)
• #define variable_name will always be present
• A variable may optionally have a value (e.g. { 300 })
• The variable value (if present) may be of all possible types (Text, Number or Vector)
• A line may have a leading comment, either after the value or directly after the variable_name

I have been managing to create the following expression successfully up to the point of the optional variable value or optional comment:

/^(\/\/)?(#define)\s(\w+)\s?(.*[\/\/]?)?

The expression can be tested here: https://regex101.com/r/krZB71/3/

The problem I have is visible in the Group 4 of the fifth (5) and sixth (6) Match, the value and leading comment end up being grouped together... My aim is to separately group the variable_name, the optional value, the optional leading comment

I basically need help for the part after the \s?:

/^(\/\/)?(#define)\s(\w+)\s? xxxxxxxxxx

Any help highly appreciated

I found that using the following expression separates the variable and the comment:

^(\/\/)?(#define)\s(\w+)\s?(.*?)(\/\/.*?)?$

You could make the pattern a bit more specify and use optional capture groups to get the separate values.

^(\/\/)?(#define)\s(\w+)(?:\s?({[^{}]*})?\s?(\/\/\s?(.*))?)?

• ^ Start of string
• (\/\/)? Optional group 1, match //
• (#define)\s Capture group 2, match #define and whitespace char
• (\w+) Capture group 3 Match 1+ word chars
• (?: Non capture group
• \s? Match optional whitespace char
• ( Optional capture group 4
  • {[^{}]*} Match {...}
• )? Close group 4 and make it optional
• \s? Match optional whitespace char
• ( Optional capture group 5
  • \/\/\s? Match // then optional whitespace char
  • (.*) Capture group 6 match any char except a newline
• )? Close group 5 and make it optional
• )? Close non capture group and make it optional so the whole last part is optional

Regex demo

Note that \s also matches a newline. If you want to match whitespace chars without the newlines you could match tabs or spaces [\t ] or match a whitespace char except the newlines [^\S\r\n].