How to convert std::string to std::u32string in C++11?

Question

I am working with Unicode in C++11 & I am right now unable to convert std::string to std::u32string.

My code is as follows:

#include <iostream>
#include <string>
#include <locale>
#include "unicode/unistr.h"
#include "unicode/ustream.h"

int main()
{
    constexpr char locale_name[] = "";
    setlocale( LC_ALL, locale_name );
    std::locale::global(std::locale(locale_name));
    std::ios_base::sync_with_stdio(false);
    std::wcin.imbue(std::locale());
    std::wcout.imbue(std::locale());

    std::string str="hello☺😆";

    std::u32string s(str.begin(),str.end());

    icu::UnicodeString ustr = icu::UnicodeString::fromUTF32(reinterpret_cast<const UChar32 *>(s.c_str()), s.size());
    std::cout << "Unicode string is: " << ustr << std::endl;

    std::cout << "Size of unicode string = " << ustr.countChar32() << std::endl;

    std::cout << "Individual characters of the string are:" << std::endl;
    for(int i=0; i < ustr.countChar32(); i++)
      std::cout << icu::UnicodeString(ustr.char32At(i)) << std::endl;

    return 0;
}

On executing the output is: (which is not expected)

Unicode string is: hello�������
Size of unicode string = 12
Individual characters of the string are:
h
e
l
l
o
�
�
�
�
�
�
�

Please suggest if any ICU library function exists for this

Answer 1

Thanks everybody for help!

Using these 2 links, I was able to found some relevant functions:

• https://en.cppreference.com/w/cpp/string/multibyte/mbrtoc32

• How to convert a Unicode code point to characters in C++ using ICU?

I tried using codecvt functions, but I got the error:

fatal error: codecvt: No such file or directory
 #include <codecvt>
                   ^
compilation terminated.

So, I skipped that & on further searching, I found mbrtoc32() function which works:)

This is the working code:

#include <iostream>
#include <string>
#include <locale>
#include "unicode/unistr.h"
#include "unicode/ustream.h"
#include <cassert>
#include <cwchar>
#include <uchar.h>

int main()
{
    constexpr char locale_name[] = "";
    setlocale( LC_ALL, locale_name );
    std::locale::global(std::locale(locale_name));
    std::ios_base::sync_with_stdio(false);
    std::wcin.imbue(std::locale());
    std::wcout.imbue(std::locale());

    std::string str;
    std::cin >> str;
    //For example, the input string is "hello☺😆"

    std::mbstate_t state{}; // zero-initialized to initial state
    char32_t c32;
    const char *ptr = str.c_str(), *end = str.c_str() + str.size() + 1;

    icu::UnicodeString ustr;

    while(std::size_t rc = mbrtoc32(&c32, ptr, end - ptr, &state))
    {
      icu::UnicodeString temp((UChar32)c32);
      ustr+=temp;
      assert(rc != (std::size_t)-3); // no surrogates in UTF-32
      if(rc == (std::size_t)-1) break;
      if(rc == (std::size_t)-2) break;
      ptr+=rc;
    }

    std::cout << "Unicode string is: " << ustr << std::endl;
    std::cout << "Size of unicode string = " << ustr.countChar32() << std::endl;
    std::cout << "Individual characters of the string are:" << std::endl;
    for(int i=0; i < ustr.countChar32(); i++)
      std::cout << icu::UnicodeString(ustr.char32At(i)) << std::endl;

    return 0;
}

The output on entering input hello☺😆 is as expected:

Unicode string is: hello☺😆
Size of unicode string = 7
Individual characters of the string are:
h
e
l
l
o
☺
😆