Natural sort in C - “array of strings, containing numbers and letters”

Question

Looking for a proven to work algorithm for production. Did see this example but not finding much else on the web or in books.

i.e. file_10.txt > file_2.txt

Thank

Answer 1

Here's a version for Qt, that also supports unicode:

int strcmpbynum(const QString& s1, const QString &s2) {
int i1 = 0; // index in string
int i2 = 0;
while (true) {
    if (s2.length() == i2) // both strings identical or s1 larger than s2
        return s1.length() == i1 ? 0 : 1;
    if (s1.length() == i1) return -1; // s1 smaller than s2

    unsigned short u1 = s1[i1].unicode();
    unsigned short u2 = s2[i2].unicode();

    if (u1 >= '0' && u1 <= '9' && u2 >= '0' && u2 <= '9') {
        // parse both numbers completely and compare them
        quint64 n1 = 0; // the parsed number
        quint64 n2 = 0;
        int l1 = 0; // length of the number
        int l2 = 0;
        do {
            ++l1;
            n1 = n1 * 10 + u1 - '0';
            if (++i1 == s1.length()) break;
            u1 = s1[i1].unicode();
        } while (u1 >= '0' && u1 <= '9');
        do {
            ++l2;
            n2 = n2 * 10 + u2 - '0';
            if (++i2 == s2.length()) break;
            u2 = s2[i2].unicode();
        } while (u2 >= '0' && u2 <= '9');
        // compare two numbers
        if (n1 < n2) return -1;
        if (n1 > n2) return 1;
        // only accept identical numbers if they also have the same length
        // (same number of leading zeros)
        if (l1 < l2) return -1;
        if (l1 > l2) return 1;
    } else {
        // compare digit with non-digit or two non-digits
        if (u1 < u2) return -1;
        if (u1 > u2) return 1;
        ++i1;
        ++i2;
    }
}

}