c++ making a unicode char from a string

Question

I have a string like this

string s = "0081";

and I need to make a one character string like this

string c = "\u0081"  

how can I make that string of length 1 from the original string of length 4?

EDIT: my mistake, "\" is not a char (1 byte) but a 2 bytes character/string? so what I have as input is a binary, 1000 0001 which is 0x81, and this is where comes my string "0081". would it be easier to go from this 0x81 to a string c = "\" whatever is that value? thanks for all the help

Answer 1

Here you go:

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

Here's the whole process, based on some code I linked to in a comment elsewhere.

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;
}

Note that this code doesn't do any error checking, so if you pass it an invalid codepoint you'll get back an invalid string.