Regex match with negative lookbehind, recursive pattern and negative lookahead

Question

I need to match this:

void function{ {  {  } }}   

(function definition with balanced parenthesis) but not this

static stTLookupTable RxTable[MAX]={
     
    {zero, one},{zero, one},{zero, one}};

I have tried to match with lookarounds with (?<![[=])({((?>[^{}]+|(?R))*)})(?!;) But this matches {zero, one} in the variable declaration.

(?<![[=]){((?>[^{}]+|(?R))*)}[^;]$ doesn't work either.

In short, I need it to match function definition, but not the array declaration, assuming array initialization starts with ]=. Does anyone know how to match the function definition alone?

PS: {((?>[^{}]+|(?R))*)} matches for balanced paranthesis

Answer 1

Assuming you are using PyPi regex module you can use

import regex
text = """void function{ {  {  } }}   
static stTLookupTable RxTable[MAX]={
     
    {zero, one},{zero, one},{zero, one}};"""

print( [x.group(3) for x in regex.finditer(r'=\s*({(?>[^{}]+|(?1))*})(*SKIP)(*F)|({((?>[^{}]+|(?2))*)})', text)] )
# => [' {  {  } }']

See the Python demo online.

Details:

• =\s*({(?>[^{}]+|(?1))*})(*SKIP)(*F):
  • = - a = char
  • \s* - zero or more whitespaces
  • ({(?>[^{}]+|(?1))*}) - a substring between balanced {...}
  • (*SKIP)(*F) - skips the match and restarts the search from the failure position
• | - or
• ({((?>[^{}]+|(?2))*)}) - Group 2 (technical, used for recursion):
  • {((?>[^{}]+|(?2))*)} - matches a {...} substring with balanced curly braces.

You need to return Group 3 from the matches.