Automatically generate struct instances

Question

Lets say the struct is defined as :

struct car {
   int registration_number;
}

I want to generate a specific number of struct instances as specified by the user.

Enter number of cars: 20
#generate 20 struct instances

I do not want to make an array inside struct but want a separate instance for every car. I cant understand what the protocol is to automatically generate instances.

car1,car2,car3......,car n

I thought I would run a loop but I cant understand how to declare new instance name everytime :

#some loop
struct car instance_name   #how to replace instance_name with actual names?

Make an array of structs. You can't create variable names at runtime. — melpomene, Dec 04 '16 at 23:04
Possible duplicate of [How to properly malloc for array of struct in C](https://stackoverflow.com/questions/19613752/how-to-properly-malloc-for-array-of-struct-in-c) — Armali, Mar 28 '18 at 06:33
Make an array of struct if size n, choice is yours to declare it static or dynamic memory allocation. — Sandeep_black, Mar 28 '18 at 07:06

score 0 · Answer 1 · answered Mar 28 '18 at 06:33

0

Make an array of structs. You can't create variable names at runtime. – melpomene

answered Mar 28 '18 at 06:33

Armali

18,255
14
57
171

score -2 · Answer 2 · edited May 23 '17 at 12:01

-2

If you don't know in advance how many car instances you will need, a handy solution is to use malloc to reserve more memory on the fly.

carArray = (struct car**) malloc(numberOfCars*sizeOf(struct car));

for (int i =0; i < numberOfCars; i++)
    carArray[i] = (struct car*) malloc (sizeof(struct car));

A helpful example article here

A user with a similar question here

edited May 23 '17 at 12:01

Community

1
1

answered Dec 04 '16 at 23:47

Luminaire

334
6
11

2

Don't cast `malloc()`. And in this case either your cast or your `sizeof` expression is wrong. (Why use a 2-level structure anyway?) – melpomene Dec 04 '16 at 23:49
5

Better: `struct car *cars; ... cars = malloc(num * sizeof *cars); ... cars[i].registration_number = 42;` – melpomene Dec 04 '16 at 23:52

Automatically generate struct instances

2 Answers2

Linked