0

I'm compiling this with VS 2022 C++ compiler, as "ISO C++20 Standard (/std:c++20)" for a Debug configuration.

How come this throws the following std::regex_error:

regex_error(error_backref): The expression contained an invalid back reference.

std::wregex re;
bool bCaseSens = true;

re.assign(L"FilE", 
    std::wregex::ECMAScript | 
    std::wregex::nosubs |
    std::wregex::optimize |
    (bCaseSens ? 0 : std::wregex::icase)
);

but this compiles and works fine?

std::wregex re;
bool bCaseSens = true;

re.assign(L"FilE", 
    std::wregex::ECMAScript | 
    std::wregex::nosubs |
    std::wregex::optimize
);

PS. Note that the Release build doesn't throw that exception.

PS2. Also tried with older versions of C++ standard with the same effects.

Improve this question
3
  • In the first case, it's probably assign (4) because the 0 converts the expression to a std::size_t (or something convertible into that), but in the second case it's assign (3). q.v. en.cppreference.com/w/cpp/regex/basic_regex/assign.html Commented Oct 29 at 19:13
  • 1
    To add to the comment by @Eljay -- the type of the expression (bCaseSens ? 0 : std::wregex::icase) is int, not std::regex::syntax_option_type. That means that the type of the result of the sequence of | operators is also int, and not syntax_option_type, so the compiler picks an inappropriate overload of assign. Commented Oct 29 at 19:29
  • I've had bad luck using assign() on regex variables that haven't been initialized. It's better to do an initialize declaration std::wregex re(""); then re.assign() What I ended up adopting was to use a copy assign method, ex : typedef boost::wregex X_regex;\n #define MAKEREGEX(str,options) boost::wregex(str,options)\n X_regex re = MAKEREGEX( "\\bFilE\\b", ECMAScript | nosubs | optimize | (bCaseSens ? 0 : icase)); Commented Oct 30 at 18:36
Related questions
3457
What's the problem with "using namespace std;"?
738
What is the easiest way to initialize a std::vector with hardcoded elements?
0
initializing 2d std::array in a class works in release build but not in debug
Load 6 more related questions Show fewer related questions

0

Reset to default

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.