how to detect “​” (combination of unicode) in c++ string

Question

I am trying to detect some of the combination of Unicode character (like ​) to cleanup the string, For a single Unicode character it is detecting but combination of Unicod

Answer 1

OK, following on from the comments above, I think it's highly likely that the input string is in UTF-8 (after all, in an HTML context, what else would it be?).

On that basis, I humbly submit this:

#include <string>
#include <codecvt>
#include <locale>

std::string narrow (const std::wstring& ws)
{
    std::wstring_convert <std::codecvt_utf8 <wchar_t>, wchar_t> convert;
    return convert.to_bytes (ws);
}

std::wstring widen (const std::string& s)
{
    std::wstring_convert <std::codecvt_utf8 <wchar_t>, wchar_t> convert;
    return convert.from_bytes (s);
}

std::string detect_Unicode (const std::string& s)
{ 
    std::wstring ws = widen (s);
    if (ws.empty() || ws.find_first_not_of (L" \t\n\r\f\v\u00A0\u00C2\u00E2\u20AC\u2039") != std::wstring::npos)
        return " ";
    return s;
}

#include <iostream>

int main ()
{
    std::cout << narrow (L"\u00A0 \u00C2 \u00E2 \u20AC \u2039\n\n");
    std::cout << "0.\t\"" << detect_Unicode (u8"abcde") << "\"\n";
    std::cout << "1.\t\"" << detect_Unicode (u8" ​    ​ ") << "\"\n";
    std::cout << "2.\t\"" << detect_Unicode (u8"are   there is something    ​ combination    ​") << "\"\n";
    std::cout << "3.\t\"" << detect_Unicode (u8" Â Â ") << "\"\n";
    std::cout << "4.\t\"" << detect_Unicode (u8"​    ​") << "\"\n";
    std::cout << "5.\t\"" << detect_Unicode (u8"Â Â â â") << "\"\n";
}

Output:

  Â â € ‹

0.  " "
1.  " ​    ​ "
2.  " "
3.  " Â Â "
4.  "​    ​"
5.  "Â Â â â"

Now this is not the output the OP expects, but I think that's simply because the logic (as opposed to the implementation) of detect_Unicode() looks flawed. The point here is that converting the input string to a wide string means that you can use standard basic_string operations on it reliably, because there are no multibyte issues now.

An alternative, slightly radical, implementation of detect_Unicode() might be:

for (auto wide_char : ws)
{
    if (wide_char > 0xff)
        return " ";
}
return s;

But really, now you have a wide string to hand in detect_Unicode, anything is possible, so go wild OP.

Other notes:

• std::codecvt is deprecated in C++17, but since there is no other obvious choice you might as well run with it. You can always change the implementations of narrow and widen if it comes to it.
• Depending on platform, std::wstring might not be the best choice but it's probably fine. You could also look at std::u16string and std::u32string.

Live demo.

Inspiration taken from here.