将Unicode值分配给char

Question

My code includes a loop in which checks every character of a std::string , assign it to a char variable, which fails its assertion when -1 >= c >= 255 .

It is a method from a JSON parser class that it's not mine:

static std::string UnescapeJSONString(const std::string& str)
{
    std::string s = "";

    for (int i = 0; i < str.length(); i++)
    {
        char c = str[i]; // << HERE FAILS WHEN 'É' CHARACTER
        if ((c == '\\') && (i + 1 < str.length()))
        {
            int skip_ahead = 1;
            unsigned int hex;
            std::string hex_str;

            switch (str[i+1])
            {
                case '"' :  s.push_back('\"'); break;
                case '\\':  s.push_back('\\'); break;
                case '/' :  s.push_back('/'); break;
                case 't' :  s.push_back('\t'); break;
                case 'n' :  s.push_back('\n'); break;
                case 'r' :  s.push_back('\r'); break;
                case 'b' :  s.push_back('\b'); break;
                case 'f' :  s.push_back('\f'); break;
                case 'u' :  skip_ahead = 5;
                    hex_str = str.substr(i + 4, 2);
                    hex = (unsigned int)std::strtoul(hex_str.c_str(), nullptr, 16);
                    s.push_back((char)hex);
                    break;

                default: break;
            }

            i += skip_ahead;
        }
        else
            s.push_back(c);
    }

    return Trim(s);
}

How can I assign a Unicode value to a char? In this case the value is É , and the code is not ready to receive such a characters.

This is included into a dll library, and is giving me this error:

Answer 1

The std::string doesn't use Unicode. This is evident because there is a method c_str that lets you get a char array from the std::string.

Answering your question, your test is wrong:

-1 >= c && c >= 255

It should be:

-1 <= c && c <= 255

But you can't get c anywhere near 255 since the char is signed. If you want to get 255 out a char it needs to be

unsigned char

This will not let you reach -1 though.

Read about char*'s here:

http://www.cplusplus.com/doc/tutorial/variables/

see char arrays here:

http://www.cplusplus.com/doc/tutorial/ntcs/

see std::string here:

http://www.cplusplus.com/reference/string/string/