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

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< 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) |

Performs multibyte to wide conversion, using the codecvt facet supplied at construction.

1) Converts `byte` as if it was a string of length 1 to wide_string

2) Converts the null-terminated multibyte character sequence beginning at the character pointed to by `ptr` to wide_string

3) Converts the narrow string `str` to wide_string.

4) Converts the narrow multibyte character sequence `[first, last)` to wide_string

In all cases, the conversion begins in initial shift state, unless non-initial starting state was provided to this `wstring_convert` constructor. The number of characters converted and the final value of the conversion state are remembered and can be accessed with state() and converted()

### Return value

A `wide_string` object containing the results of multibyte to wide conversion. If the conversion failed and there was a user-supplied wide-error string provided to the constructor of this `wstring_convert`, returns that wide-error string.

### Exceptions

If this `wstring_convert` object was constructed without a user-supplied wide-error string, throws std::range_error on conversion failure.

### Example

Run this code

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

    int main()
    {
        std::string utf8 =  u8"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 << "UTF16 conversion produced " << utf16.size() << " code units:\n";
        for (char16_t c : utf16)
            std::cout << std::hex << std::showbase << c << '\n';

        // 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 << "UTF32 conversion produced " << std::dec << utf32.size() << " code units:\n";
        for (char32_t c : utf32)
            std::cout << std::hex << std::showbase << c << '\n';
    }

Output:

    UTF16 conversion produced 5 code units:
    0x7a
    0xdf
    0x6c34
    0xd834
    0xdd0b
    UTF32 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,State>`)

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