Regex search for Text then match elements - c++

Question

I would like to install a condition. I have already tried a lot but without success. Would someone be so kind and would help me?
My goal: if SharedKeys true then match elements(A B C D).
SharedKeys = "A","B","C","D"
Regex: (?!\")[A-Z]*?(?=\")
Match elements: A B C D
Update: (SharedKeys)?(?(1)|(?!\")[A-Z]*?(?=\"))
Match elements: SharedKeys A B C D
Link: https://regex101.com/r/WFxZh4/1
I think i have now what i needed, maybe helps others.
SharedKeys = "A","B","C","D"
BlaBla = "B", "B", "C"
Result: (SharedKeys|BlaBla)?(?(1)|(?!\")[A-Z]*?(?=\"))
Match elements: SharedKeys A B C D BlaBla B B C
Result for c++: [A-Za-z]+|(?!\")[A-Z]*?(?=\") (std::regex)

Answer 1

with std::regex:
std::string s1( R"(SharedKeys = "A","B","C","D")" );
std::regex rx( "(SharedKeys)?(?(1)|[A-Z](?=\\\"))" );
std::match_results< std::string::const_iterator > mr;
while( std::regex_search( s1, mr, rx ) ){
std::cout << mr.str() << '\n';
s1 = mr.suffix().str();
}
the output:
terminate called after throwing an instance of 'std::regex_error'
what(): Invalid special open parenthesis. Aborted (core dumped)
with boost::regex:
std::string s1( R"(SharedKeys = "A","B","C","D")" );
boost::regex rx( "(SharedKeys)?(?(1)|[A-Z](?=\\\"))" );
boost::match_results< std::string::const_iterator > mr;
while( boost::regex_search( s1, mr, rx ) ){
std::cout << mr.str() << '\n';
s1 = mr.suffix().str();
}
the output:
SharedKeys
A
B
C
D
here you can see the difference between this two flavors:
source of the screenshot
Note. The std::regex is buggy especially with gcc version 6.3.0 and lower versions