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    Qsort to compare strings for alphabetical order - C language

    I'm using the qsort() that comes with the library to sort an array of structures of strings.

    It's essentially an array of strings but with a structure that is containing the array.

    For example:

    typedef struct node {
    char name[MAX_SIZE + 1];
    } Node;

    Then my array of nodes that contains the names would be:

    Node nodes_list[MAX_SIZE + 1];

    My question is, I want to sort nodes_list so when I print the following:

    for (i = 0; i < size; i++) {
    printf("%s\n", nodes_list[i].name);

    it prints all the names in alphabetical order.

    I would like to do sort the list using qsort and my comparator function is this:

    int compare(const void *a, const void *b) {
    const char **ia = (const char **)a;
    const char **ib = (const char **)b;
    return strcmp(*ia, *ib);

    when I run the function with qsort:

    qsort(nodes_list, size, sizeof(Node), compare);

    I get a segmentation fault (core dumped).

    I know I am getting a seg. fault with this snippet of code because without it, I can print the list of names fine. Not sorted of course.
  2. #2
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    Cast 'const void *' to a pointer of Node-element before assign it to 'const char **'.

    int compare(const void *a, const void *b) {
        const char **ia = ((Node *)a)->name;
        const char **ib = ((Node *)b)->name;
        return strcmp(*ia, *ib);
  4. #3
  5. Contributed User
    Devshed Specialist (4000 - 4499 posts)

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    You're not sorting an array of char pointers, you're sorting an array of Nodes.

    So the cast in your compare functions is wrong.

    Try say
    const Node *ia = a;

    Then use
    in the strcmp
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper

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