CODEWITHSUNDEEP
carraysstruct
EUS
EUS

Reputation: 422

Difference between these two struct usages

When using structs in functions, I have come along with two ways of passing them as arguments, and I don't know which one is better to use.

#include <stdio.h>

typedef struct Person{
    int age;
    int id;
} person;

static void foo(person *p1);

int main()
{
    person per1;
    person per2[1];

    foo(&per1); /*1*/
    foo(per2); /*2*/

    printf("per1. Age: %i; id: %i\n",per1.age,per1.id);
    printf("per2. Age: %i; id: %i\n",per2->age,per2->id);

    return 0;
}
static void foo(person *p1)
{
    p1->age=10;
    p1->id=123;
}

The use case is for only one instance of the struct. If no more than one is needed, which one is better, in terms of performance and sense of usage, passing the address of the generic struct declaration, or passing a unitary array of the struct that will decay to a pointer?

Upvotes: 1

Views: 82

Answers (2)

Brennan Vincent
Brennan Vincent

Reputation: 10665

Any modern compiler will produce identical machine code in each case, so there is no performance concern. (See Godbolt).

Since there is no performance difference, do it the way that best expresses your intent. Your intent is to have one object, and pass the address of that one object to your function. So just do that (i.e., your first option). Creating a 1-element array for no reason just makes things confusing.

Upvotes: 8

Daniel
Daniel

Reputation: 144

Both are correct. Which one is better depends on your needs.

per1 is of type person (which in torn is a typedef of struct Person), so if you want to pass it, you pass its address (as you did using the& operator).

per2 is an array of persons, so its type is actually an array address and that is why you can pass it as-is. If you have no need for an array of person, use the first option.

Upvotes: 1

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