convert ucs(Universal Character Set) character to unicode?

Question

I am reading code from somebody, I happended to see code as follow.

According to comment, this function is to Convert a UCS character to an UTF-8 string. But what is ucs character, what is the rule to convert ucs to unicode, where can I find the documents?

/*
 * Convert a UCS character to an UTF-8 string
 *
 * Returns the string length of the result
 */
size_t
tUcs2Utf8(ULONG ulChar, char *szResult, size_t tMaxResultLen)
{
    if (szResult == NULL || tMaxResultLen == 0) {
        return 0;
    }

    if (ulChar < 0x80 && tMaxResultLen >= 2) {
        szResult[0] = (char)ulChar;
        szResult[1] = '\0';
        return 1;
    }
    if (ulChar < 0x800 && tMaxResultLen >= 3) {
        szResult[0] = (char)(0xc0 | ulChar >> 6);
        szResult[1] = (char)(0x80 | (ulChar & 0x3f));
        szResult[2] = '\0';
        return 2;
    }
    if (ulChar < 0x10000 && tMaxResultLen >= 4) {
        szResult[0] = (char)(0xe0 | ulChar >> 12);
        szResult[1] = (char)(0x80 | (ulChar >> 6 & 0x3f));
        szResult[2] = (char)(0x80 | (ulChar & 0x3f));
        szResult[3] = '\0';
        return 3;
    }
    if (ulChar < 0x200000 && tMaxResultLen >= 5) {
        szResult[0] = (char)(0xf0 | ulChar >> 18);
        szResult[1] = (char)(0x80 | (ulChar >> 12 & 0x3f));
        szResult[2] = (char)(0x80 | (ulChar >> 6 & 0x3f));
        szResult[3] = (char)(0x80 | (ulChar & 0x3f));
        szResult[4] = '\0';
        return 4;
    }
    szResult[0] = '\0';
    return 0;
} /* end of tUcs2Utf8 */

Answer 1

Universal Character Set is an ISO standard. It defines the same characters as Unicode, so there's no need for character conversion. Every version of UCS is essentially a small subset of a certain version of the Unicode standard. New characters are first added to Unicode and every so often, UCS is synchronized with Unicode. Appendix C of the Unicode standard contains a table that shows the relationship between different versions.

Also note that the code you posted uses a non-standard upper limit of 0x200000. This should be changed to 0x110000.