Message Queue Insertion Example

#include <stdio.h>
#include <stdlib.h>

#define NODES 13

struct node{
    struct node *next;
    int ts;
    int nid;
};

typedef struct node ncmsg;

void printList(ncmsg *head) {
    ncmsg *temp = head;
    int p = 0;
    while (temp != NULL) {
        printf("(%d, %d)\t", temp -> nid, temp -> ts);
        p++;
        if (p % 8 == 0) printf("\n");
        temp = temp -> next;
    }
    printf("\nThe list is shown above.\n");
}

void insertMessage(ncmsg **head, ncmsg *newMsg) {
    if (*head == NULL) {
        printf("A.\n");
        *head = newMsg;
    } else {
        ncmsg *temp = *head;
        if (
            (newMsg -> ts) < (temp -> ts) || (
                (newMsg -> ts) == (temp -> ts) &&
                (newMsg -> nid) < (temp -> nid)
            )
        ) { // if the new message has to become the head
            printf("B.\n");
            newMsg -> next = temp;
            *head = newMsg;
        } else { // if the new message goes after the head somewhere
            printf("C.\n");
            while (
                (temp -> next) != NULL && (
                    (newMsg -> ts) > (temp -> next -> ts) || (
                        (newMsg -> ts) == (temp -> next -> ts) &&
                        (newMsg -> nid) > (temp -> next -> nid)
                    )
                )
            ) {
                temp = temp -> next;
            }
            newMsg -> next = temp -> next;
            temp -> next = newMsg;
        }
    }
}

void popHead(ncmsg **head) {
    if ((*head) -> next != NULL) {
        *head = ((*head) -> next);
    }
    else {
        perror("Head is the sole element of the list, popping it will destroy the list!\nAborting!\n");
    }
}

int main() {
    srand(11091996);
    int i, j;
    int tsArr[NODES];

    for (i = 0; i < NODES; i++) tsArr[i] = 1;

    ncmsg *temp, *head;
    /*
    head = (ncmsg *) malloc(sizeof(ncmsg));
    head -> ts = 0;
    head -> nid = 0;
    head -> next = NULL;
    */
    head = NULL;

    for (i = 0; i < 64; i++) {
        j = (rand() % NODES) + 1;

        temp = (ncmsg *) malloc(sizeof(ncmsg));

        temp -> ts = tsArr[j - 1];
        tsArr[j - 1]++;
        temp -> nid = j;
        temp -> next = NULL;

        printf("New message: (%d, %d). ", temp -> nid, temp -> ts);
        insertMessage(&head, temp);
        //printList(head);
    }

    printList(head);
    printf("Now popping off the head node...\n");
    popHead(&head);
    printList(head);
    printf("Done.\n");

    return 0;
}