JSON string encoder, from STL string to JSON

gistfile1.cpp

static inline std::string jsonEscape(std::string &str)
{
	std::string escaped = "\"";
	char buf[16];
	unsigned int i;

	for (i = 0; i < str.size(); i++)
	{
		if (str[i] == 34) escaped += '\\';

		if (str[i] >= 32 && str[i] <= 126) escaped += str[i];
		else {
			// UTF8
			unsigned char nums[] = {0,0,0,(unsigned char)str[i]};

			unsigned char charsLeft = str.size() - i;
			if ((nums[3] & 0xF8) == 0xF0) {
				if (charsLeft < 4) break;

				nums[0] = str[i] & 0x0F;
				nums[1] = str[i+1] & 0x1F;
				nums[2] = str[i+2] & 0x3F;
				nums[3] = str[i+3] & 0x7F;
				i += 3;
			}
			else if ((nums[3] & 0xF0) == 0xE0) {
				if (charsLeft < 3) break;

				nums[1] = str[i] & 0x1F;
				nums[2] = str[i+1] & 0x3F;
				nums[3] = str[i+2] & 0x7F;

				i += 2;
			}
			else if ((nums[3] & 0xE0) == 0xC0) {
				if (charsLeft < 2) break;

				nums[2] = str[i] & 0x3F;
				nums[3] = str[i+1] & 0x7F;

				i += 1;
			}
			else {
				// 1-char or invalid stuff
				// Not UTF-8... BROKEN
				nums[3] = str[i] & 0x7F;
			}

			unsigned short cCode = (nums[0] << 15) + (nums[1] << 11) + (nums[2] << 6) + (nums[3]);

			sprintf_s(buf, 16, "\\u%.4X", cCode);
			escaped += buf;
		}
	}

	escaped += "\"";

	return escaped;
}