Regular Expressions not working

[crimsonzero2]

Hi, I have this bit of code that I found here:
https://www.youtube.com/watch?v=v_8rdQjOuxw
and at first regex would work, but then when I hit "[]" it wouldn't. Here's the code:

#include <iostream>
#include <string>
#include <regex>

using namespace std;

int main()
{
    string str;
    while(true)
    {
        cin >> str;

        regex e("ab[cd]*");

        bool match = regex_match(str, e);

        cout << (match? "Matched" : "Not Matched") << endl << endl;
    }
    return 0;
}

Can anyone explain to me why it won't? Thank you.

[keskiverto]

What was the exact input that doesn't give expected result?

[crimsonzero2]

Any input from the video. For example typing "ab" into the program should output "matched" but instead it gives me a regex_error statement and crashes the program.