How to access an element in the structure which not the first - Qsort

Question

I am trying to sort the following structure. I am using the qsort to order the books according to date publish in order of the newest first. I completely don\'t understand why t

Answer 1

Here is an example of a multikey sort:

int
cmp_multikey(const void *a,const void *b)
{
    const struct book *booka = a;
    const struct book *bookb = b;
    int cmp;

    do {
        // sort by year published
        cmp = booka->year_published - bookb->year_published;
        if (cmp)
            break;

        // sort by author
        cmp = strcmp(booka->author,bookb->author);
        if (cmp)
            break;

        // sort by title
        cmp = strcmp(booka->name,bookb->name);
        if (cmp)
            break;
    } while (0);

    return cmp;
}

---

Invoke with:

qsort(books,numberofbooks,sizeof(struct book),cmp_multikey);

---

Some other tips ...

[As others have mentioned] Never use gets. Use a switch/case instead of an if/else ladder.

Try to avoid intermixing scanf and fgets.

Personally, I prefer to [always] use fgets. Here is a [safe] replacement for gets and a replacment for scanf("%d",&num);:

int
getstr(const char *prompt,char *buf,int buflen)
{
    char *cp;

    printf("%s",prompt);
    fflush(stdout);

    cp = fgets(buf,buflen,stdin);
    if (cp == NULL) {
        fprintf(stderr,"unexpected EOF\n");
        exit(1);
    }

    // find newline
    cp = strchr(buf,'\n');

    // ensure we had enough space
    if (cp == NULL) {
        fprintf(stderr,"response too large for buffer\n");
        exit(1);
    }

    // strip newline
    *cp = 0;
}

int
getnum(const char *prompt)
{
    char buf[1000];
    int num;

    getstr(prompt,buf,sizeof(buf));

    num = atoi(buf);

    return num;
}