C Structs and Pointers

Structures and Pointers

You can use pointers with structs to make your code more efficient, especially when passing structs to functions or changing their values.

To use a pointer to a struct, just add the * symbol, like you would with other data types.

To access its members, you must use the -> operator instead of the dot . syntax:

// Define a struct
struct Car {
  char brand[30];
  int year;
};

int main() {
  struct Car car = {"Toyota", 2020};

  // Declare a pointer to the struct
  struct Car *ptr = &car;

  // Access members using the -> operator
  printf("Brand: %s\n", ptr->brand);
  printf("Year: %d\n", ptr->year);

  return 0;
}

ptr->brand is a shorter way to write (*ptr).brand: it goes to the struct that ptr points to, and gets its brand member.

Passing Struct Pointers to Functions

Just like in the Pass By Reference chapter, you can pass a pointer to a struct to a function, so the function can change the original struct:

struct Car {
  char brand[30];
  int year;
};

// Function that takes a pointer to a Car struct and updates the year
void updateYear(struct Car *c) {
  c->year = 2025;  // Change the year
}

int main() {
  struct Car myCar = {"Toyota", 2020};

  updateYear(&myCar);  // Pass a pointer so the function can change the year

  printf("Brand: %s\n", myCar.brand);
  printf("Year: %d\n", myCar.year);

  return 0;
}

Why Use Struct Pointers?

Using pointers with structs is helpful when:

• You want to avoid copying large amounts of data.
  Instead of copying a whole struct, you can just pass a pointer. This makes your program faster and uses less memory.


• You want to change values inside a function.
  If you pass a pointer to a struct into a function, the function can change the original values.


• You want to create structs dynamically using memory allocation.
  With pointers, you can use malloc() to create structs while the program is running.
  You will learn more about memory management in a later chapter.