（C ++）确定不匹配的正则表达式捕获组

Question

I want to check if a password meets the following requirements:

It should:

• contain at least 1 small letter (ASCII 97-122)
• contain at least 1 letter (65-90)
• contain at least 1 digit
• contain at least 1 special character (33-47, 58-64, 91-96, 123-126)
• have a length between 8 and 20 characters

It should also tell me which of these requirements did it not meet.

---

Given the following expression I can validate it with regex_match() from std::regex library

regex re("^(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])(?=.*[!-/:-@[-`{-~])(\\S){8,20}$");

But this way I can only know if it matches or does not, as it returns a boolean

Given this, I tried iterating over the match_results like below, after adding some capture groups to the expression.

std::string str("AAAaaa111$$$");
std::regex rx("^((?=.*[a-z]).*)((?=.*[A-Z]).*)((?=.*[0-9]).*)((?=.*[!-/:-@[-`{-~]).*)(\\S){8,20}$");
std::match_results< std::string::const_iterator > mr;

std::regex_search(str, mr, rx);

std::cout << "size: " << mr.size() << '\n'; // 6 or 0 only ?
for (int i = 0; i < mr.size(); i++) {
    std::cout << "index: " << i << "\t --> \t" << mr.str(i) << endl;
}

if (regex_match(str, rx)) {
    cout << "tests passed" << endl;
}
else {
    cout << "tests failed" << endl;
}

And it produced the following output:

size: 6
index: 0         -->    AAAaaa111$$$
index: 1         -->    AA
index: 2         -->    Aa
index: 3         -->
index: 4         -->
index: 5         -->    $
tests passed
Press any key to continue . . .

What I'd like to achieve is to tell which of the groups failed to match. For example for input: SamplePassword1 only the 4th group would fail to match, as it does not contain a special character. The user could then be notified which specific requirement/s did the password not meet. Accordingly, SamplePassword1$ would have a match in each of the groups and pass.

Is this task achievable using a single regular expression rather than having a separete one for each of the requirements?

---

I came across a somewhat similar question here , but it's in C# .NET and uses named capturing groups.

 var re = new Regex("((?<a>a)|(?<b>b))"); var ma = re.Match("a"); Console.WriteLine("a in a: " + ma.Groups["a"].Success); //true Console.WriteLine("b in a: " + ma.Groups["b"].Success); //false 

Answer 1

std::regex rx("^((?=.*[a-z]))?((?=.*[A-Z]))?((?=.*[0-9]))?((?=.*[!-/:-@[-`{-~]))?(\\S){8,20}$");

and check with mr[i].first == str.end() . Demo

That said, recall the saying :

Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems.