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
– melpomene, Commented Dec 4, 2016 at 23:04
Possible duplicate of How to properly malloc for array of struct in C — Armali
– Armali, Commented Mar 28, 2018 at 6:33
Make an array of struct if size n, choice is yours to declare it static or dynamic memory allocation. — Sandeep_black
– Sandeep_black, Commented Mar 28, 2018 at 7:06

Armali · Accepted Answer · 2018-03-28 06:33:23Z

0

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

answered Mar 28, 2018 at 6:33

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Armali

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Community · Accepted Answer · 2017-05-23 12:01:43Z

-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, 2017 at 12:01

CommunityBot

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answered Dec 4, 2016 at 23:47

Luminaire

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2 Comments

melpomene Over a year ago

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 Over a year ago

Better: struct car *cars; ... cars = malloc(num * sizeof *cars); ... cars[i].registration_number = 42;

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