get_codepoint()

template<typename BasicJsonType , typename InputAdapterType >

int nlohmann::detail::lexer< BasicJsonType, InputAdapterType >::get_codepoint ( )

inlineprivate

get codepoint from 4 hex characters following \u

For input "\u c1 c2 c3 c4" the codepoint is: (c1 * 0x1000) + (c2 * 0x0100) + (c3 * 0x0010) + c4 = (c1 << 12) + (c2 << 8) + (c3 << 4) + (c4 << 0)

Furthermore, the possible characters '0'..'9', 'A'..'F', and 'a'..'f' must be converted to the integers 0x0..0x9, 0xA..0xF, 0xA..0xF, resp. The conversion is done by subtracting the offset (0x30, 0x37, and 0x57) between the ASCII value of the character and the desired integer value.

Returns

codepoint (0x0000..0xFFFF) or -1 in case of an error (e.g. EOF or non-hex character)

Definition at line 6749 of file json.hpp.

    {
        // this function only makes sense after reading `\u`
        JSON_ASSERT(current == 'u');
        int codepoint = 0;
        const auto factors = { 12u, 8u, 4u, 0u };
 
        for (const auto factor : factors)
        {
            get();
 
            if (current >= '0' && current <= '9')
            {
                codepoint += static_cast<int>((static_cast<unsigned int>(current) - 0x30u) << factor);
            }
 
            else if (current >= 'A' && current <= 'F')
            {
                codepoint += static_cast<int>((static_cast<unsigned int>(current) - 0x37u) << factor);
            }
 
            else if (current >= 'a' && current <= 'f')
            {
                codepoint += static_cast<int>((static_cast<unsigned int>(current) - 0x57u) << factor);
            }
 
            else
            {
                return -1;
            }
        }
 
        JSON_ASSERT(0x0000 <= codepoint && codepoint <= 0xFFFF);
        return codepoint;
    }