C ++從字符串中制作一個Unicode字符

Question

我有這樣的字符串

string s = "0081";

我需要像這樣制作一個字符串

string c = "\u0081"  

如何從長度為4的原始字符串中提取長度為1的字符串？

編輯：我的錯誤，“ \\ u0081”不是char（1字節），而是2字節的字符/字符串？ 所以我輸入的是二進制數1000 0001，即0x81，這就是我的字符串“ 0081”的來源。 從0x81到字符串c =“ \\ u0081”會更容易嗎？ 感謝所有的幫助

Answer 1

干得好：

unsigned int x;
std::stringstream ss;
ss << std::hex << "1081";
ss >> x;

wchar_t wc1 = x;
wchar_t wc2 = L'\u1081';

assert(wc1 == wc2);

std::wstring ws(1, wc);

Answer 2

這是整個過程，基於我在其他注釋中鏈接的一些代碼。

string s = "0081";
long codepoint = strtol(s.c_str(), NULL, 16);
string c = CodepointToUTF8(codepoint);

std::string CodepointToUTF8(long codepoint)
{
    std::string out;
    if (codepoint <= 0x7f)
        out.append(1, static_cast<char>(codepoint));
    else if (codepoint <= 0x7ff)
    {
        out.append(1, static_cast<char>(0xc0 | ((codepoint >> 6) & 0x1f)));
        out.append(1, static_cast<char>(0x80 | (codepoint & 0x3f)));
    }
    else if (codepoint <= 0xffff)
    {
        out.append(1, static_cast<char>(0xe0 | ((codepoint >> 12) & 0x0f)));
        out.append(1, static_cast<char>(0x80 | ((codepoint >> 6) & 0x3f)));
        out.append(1, static_cast<char>(0x80 | (codepoint & 0x3f)));
    }
    else
    {
        out.append(1, static_cast<char>(0xf0 | ((codepoint >> 18) & 0x07)));
        out.append(1, static_cast<char>(0x80 | ((codepoint >> 12) & 0x3f)));
        out.append(1, static_cast<char>(0x80 | ((codepoint >> 6) & 0x3f)));
        out.append(1, static_cast<char>(0x80 | (codepoint & 0x3f)));
    }
    return out;
}

請注意，此代碼不會進行任何錯誤檢查，因此，如果將無效的代碼點傳遞給它，則會返回無效的字符串。