# std::wstring_convert<Codecvt,Elem,Wide_alloc,Byte_alloc>::from_bytes

From cppreference.com
< cpp‎ | locale‎ | wstring convert

Defined in header `<locale>` |  |
wide_string from_bytes( char byte ); | (1) |
wide_string from_bytes( const char* ptr ); | (2) |
wide_string from_bytes( const byte_string& str ); | (3) |
wide_string from_bytes( const char* first, const char* last ); | (4) |

Converts a byte sequence to a wide string using the facet pointed to by `cvtptr`﻿.

1) The byte sequence only consists of one element byte.
2) The byte sequence is the null-terminated sequence beginning at ptr.
3) The byte sequence is the sequence contained in str.
4) The byte sequence is the range `[`first`,` last`)`.

Before the conversion begins, if *this was not constructed with constructor overload (3), `cvtstate` will be set to its default value (the initial conversion state).

The number of input elements successfully converted will be stored in `cvtcount`﻿.

### Return value

If the conversion succeeds, returns the conversion result. Otherwise, if *this is constructed with constructor overload (4), returns `wide_err_string`.

### Exceptions

If the conversion fails and *this was not constructed with constructor overload (4), throws std::range_error.

### Example

Run this code

    #include <codecvt>
    #include <cstdint>
    #include <iostream>
    #include <locale>
    #include <string>

    int main()
    {
        std::string utf8 = "z\u00df\u6c34\U0001d10b"; // or u8"zß水𝄋"
                     // or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9d\x84\x8b";

        // the UTF-8 / UTF-16 standard conversion facet
        std::u16string utf16 =
            std::wstring_convert<std::codecvt_utf8_utf16<char16_t>,
                                 char16_t>{}.from_bytes(utf8.data());
        std::cout << "UTF-16 conversion produced " << utf16.size()
                  << " code units: " << std::showbase;
        for (char16_t c : utf16)
            std::cout << std::hex << static_cast<std::uint16_t>(c) << ' ';

        // the UTF-8 / UTF-32 standard conversion facet
        std::u32string utf32 =
            std::wstring_convert<std::codecvt_utf8<char32_t>, char32_t>{}.from_bytes(utf8);
        std::cout << "\nUTF-32 conversion produced " << std::dec
                  << utf32.size() << " code units: ";
        for (char32_t c : utf32)
            std::cout << std::hex << static_cast<std::uint32_t>(c) << ' ';
        std::cout << '\n';
    }

Output:

    UTF-16 conversion produced 5 code units: 0x7a 0xdf 0x6c34 0xd834 0xdd0b
    UTF-32 conversion produced 4 code units: 0x7a 0xdf 0x6c34 0x1d10b

### See also

to_bytes | converts a wide string into a byte string (public member function)
mbsrtowcs | converts a narrow multibyte character string to wide string, given state (function)
do_in [virtual] | converts a string from `ExternT` to `InternT`, such as when reading from file (virtual protected member function of `std::codecvt<InternT,ExternT,StateT>`)

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/locale/wstring_convert/from_bytes&oldid=177290"