问如何在iOS中将UTF-8字符串转换为wchars？

EN

// Loads UTF-8 file and converts to a UTF-16 string

bool LoadUTF8File(char const *filename, wstring &str)
{
    size_t size;
    bool rc = false;
    void *bytes = LoadFile(filename, &size);
    if(bytes != 0)
    {
        int len = MultiByteToWideChar(CP_UTF8, 0, (LPCCH)bytes, size, 0, 0);
        if(len > 0)
        {
            str.resize(len + 1);
            MultiByteToWideChar(CP_UTF8, 0, (LPCCH)bytes, size, &str[0], len);
            str[len] = '\0';
            rc = true;
        }
        delete[] bytes;
    }
    return rc;
}

// LoadFile returns the loaded file as a block of memory
// There is a 3 byte BOM which MultiByteToWideChar seems to ignore
// The text in the file is encoded as UTF-8

    char *p = "attaché";

    wstring str;
    size_t size = strlen(p);
    setlocale(LC_ALL, "");
    int len = mbstowcs(null, p, size);
    if(len > 0)
    {
        str.resize(len + 1);
        mbstowcs(&str[0], p, size);
        str[len] = '\0';
    }
    TRACE(L"%s\n", str.c_str());

    len = MultiByteToWideChar(CP_UTF8, 0, p, size, null, 0);
    if(len > 0)
    {
        str.resize(len + 1);
        MultiByteToWideChar(CP_UTF8, 0, p, size, &str[0], len);
        str[len] = '\0';
    }
    TRACE(L"%s\n", str.c_str());