dynamic memory allocation in while

Question

enum ev_type { ARRIVAL, DEP_Q0, DEP_Q1, DEP_Q2, DEP_Q3 };
struct node {
    double time;
    double duration;
    enum ev_type event;
    struct node * next;
}*evlist;
typedef struct node *nptr;
double min = 0;
void generate_new_customer(double clock, double duration)
{
    nptr newev = (nptr)malloc(sizeof(nptr));
    newev->duration = duration;
    newev->time = min;
    newev->event = ARRIVAL;

    if (evlist == NULL)
    {
        evlist = newev;
        evlist->next = NULL;
    }
    else
    {
        newev->next = evlist;
        evlist = newev;
    }
    printf("%lf\n", evlist->time);
}
int main() {
    start();
    while (1) {
        generate_new_customer(1, 6);
        if (min > 480)
            break;
        min++;
    }
    return 0;
}

I'm trying to memory allocation using function. The function working by value of min. If min increase by 480 it stops and break. I checked it. But still debug assertion failed error happen. what should I do?

It's generally considered bad style to use `typedef` to define a pointer type (except function pointers). — Barmar, Oct 30 '18 at 00:58
Welcome to Stack Overflow! [don't cast malloc](https://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc) — Barmar, Oct 30 '18 at 00:58

Craig Estey · Accepted Answer · 2018-10-30T01:25:14.013

Your malloc is incorrect. It is only allocating the size of a pointer to your struct when you need it to allocate the size of the struct itself.

Change:

nptr newev = (nptr) malloc(sizeof(nptr));

Into:

nptr newev = malloc(sizeof(struct node));

UPDATE:

I notice your function is doing a push to the front of your list. This isn't a bug, but you can simplify this a bit:

Your original code:

if (evlist == NULL) {
    evlist = newev;
    evlist->next = NULL;
}
else {
    newev->next = evlist;
    evlist = newev;
}

A slight reordering:

if (evlist == NULL) {
    evlist = newev;
    newev->next = NULL;
}
else {
    newev->next = evlist;
    evlist = newev;
}

Some further reordering:

if (evlist == NULL) {
    newev->next = NULL;
    evlist = newev;
}
else {
    newev->next = evlist;
    evlist = newev;
}

Because newev->next = NULL is inside the if clause where evlist is guaranteed to be NULL, we can change this to:

if (evlist == NULL) {
    newev->next = evlist;
    evlist = newev;
}
else {
    newev->next = evlist;
    evlist = newev;
}

Now, both the if and the else are identical. So, we can eliminate the redundancy and we have:

newev->next = evlist;
evlist = newev;

dynamic memory allocation in while

1 Answers1