0x0E-structures_typedef

0x0E. C - Structures, typedef

Resources

• 0x0D. Structures.pdf
• struct (C programming language)
• Documentation: structures
• 0x0D. Typedef and structures.pdf
• typedef
• Programming in C by Stephen Kochan - Chapter 8, Working with Structures p163-189
• The Lost Art of C Structure Packing

---

Learning Objectives

• What are structures, when, why and how to use them
• How to use typedef

---

- What are structures, when, why and how to use them

In C programming, a structure is a collection of variables that can be of different data types. It allows you to group related data items and organize them into a single unit. You can access each item individually or together as a group.

Structures are commonly used when you want to group data together and pass it as a single entity to functions or modules. They also allow you to create user-defined data types that can be used in your program.

To define a structure, you use the struct keyword followed by the name of the structure and a set of braces that contains the variables or members of the structure:

struct person {
   char name[50];
   int age;
   float salary;
};

You can then create variables of this structure type and access the members using the dot . operator:

struct person achraf;
strcpy(achraf.name, "Achraf El Khnissi");
achraf.age = 44;
achraf.salary = 1;

Structures can also be used as function parameters or return types:

struct person get_person() {
   struct person p;
   strcpy(p.name, "Achraf El Khnissi");
   p.age = 44;
   p.salary = 1;
   return p;
}

- How to use typedef

typedef is a keyword in C that allows us to create an alias for an existing data type or structure. It is useful when we want to create a new data type that represents an existing type or structure. Here's an example:

typedef struct {
    char name[20];
    int age;
} Person;

The above code creates a new data type called Person that represents the structure struct person. We can now use the Person data type to declare variables of this type:

Person achraf;
achraf.age = 44;
strcpy(achraf.name, "Achraf El Khnissi");

typedef can also be used to create aliases for existing data types. For example, the following code creates an alias for the int data type:

typedef int Integer;
Integer i = 10; /* i is an int */

---

Tasks

---

0. Django

0. Django

#include <stdio.h>
#include "dog.h"

/**
 * main - check the code
 * Return: Always 0.
 */
int main(void)
{
	struct dog my_dog;
	
	my_dog.name = "Poppy";
	my_dog.age = 3.5;
	my_dog.owner = "Bob";
	
	printf("My name is %s, and I am %.1f :) - Woof!\n", my_dog.name, my_dog.age);

	return (0);
}

Compile the code this way: gcc -Wall -pedantic -Werror -Wextra 0-main.c 0-dog.c -o a Output:

$ ./a
My name is Poppy, and I am 3.5 :) - Woof!
$

---

1. A dog is the only thing on earth that loves you more than you love yourself

1. A dog is the only thing on earth that loves you more than you love yourself

#include <stdio.h>
#include "dog.h"

/**
 * main - check the code
 * Return: Always 0.
 */
int main(void)
{
	struct dog my_dog;
    
    init_dog(&my_dog, "Poppy", 3.5, "Bob");
	printf("My name is %s, and I am %.1f :) - Woof!\n", my_dog.name, my_dog.age);
    return (0);
}

Compile the code this way: gcc -Wall -pedantic -Werror -Wextra 1-main.c 1-init_dog.c -o b Output:

$ ./b
My name is Poppy, and I am 3.5 :) - Woof!
$

---

2. A dog will teach you unconditional love. If you can have that in your life, things won't be too bad

2. A dog will teach you unconditional love. If you can have that in your life, things won't be too bad

#include <stdio.h>
#include "dog.h"

/**
 * main - check the code
 * Return: Always 0.
 */
int main(void)
{
    struct dog my_dog;
    
    init_dog(&my_dog, "Poppy", 3.5, "Bob");
    print_dog(&my_dog);
    return (0);
}

Compile the code this way: gcc -Wall -pedantic -Werror -Wextra 2-main.c 2-print_dog.c 1-init_dog.c -o c Output:

$ ./c
Name: Poppy
Age: 3.500000
Owner: Bob
$

---

3. Outside of a dog, a book is a man's best friend. Inside of a dog it's too dark to read

3. Outside of a dog, a book is a man's best friend. Inside of a dog it's too dark to read

#include <stdio.h>
#include "dog.h"

/**
 * main - check the code
 * Return: Always 0.
 */
int main(void)
{
	dog_t my_dog;
	
	my_dog.name = "Poppy";
	my_dog.age = 3.5;
	my_dog.owner = "Bob";
	

    printf("My name is %s, I am %.1f :) - Woof!\n", my_dog.name, my_dog.age);
    return (0);
}

Compile the code this way: gcc -Wall -pedantic -Werror -Wextra 3-main.c 3-dog.c -o d Output:

$ ./d
My name is Poppy, I am 3.5 :) - Woof!
$

---

4. A door is what a dog is perpetually on the wrong side of

4. A door is what a dog is perpetually on the wrong side of

#include <stdio.h>
#include "dog.h"

/**
 * main - check the code
 * Return: Always 0.
 */
int main(void)
{
    dog_t *my_dog;

    my_dog = new_dog("Poppy", 3.5, "Bob");
    printf("My name is %s, and I am %.1f :) - Woof!\n", my_dog->name, my_dog->age);
    return (0);
}

Compiled with: gcc -Wall -pedantic -Werror -Wextra 4-main.c 4-new_dog.c 3-dog.c -o e

Output:

$ ./e
My name is Poppy, and I am 3.5 :) - Woof!
$

---

5. How many legs does a dog have if you call his tail a leg? Four. Saying that a tail is a leg doesn't make it a leg

5. How many legs does a dog have if you call his tail a leg? Four. Saying that a tail is a leg doesn't make it a leg

#include <stdio.h>
#include "dog.h"

/**
 * main - check the code
 * Return: Always 0.
 */
int main(void)
{
    dog_t *my_dog;

    my_dog = new_dog("Poppy", 3.5, "Bob");
    printf("My name is %s, and I am %.1f :) - Woof!\n", my_dog->name, my_dog->age);
    free_dog(my_dog);
    return (0);
}

Compiled with: gcc -Wall -pedantic -Werror -Wextra 5-main.c 5-free_dog.c 4-new_dog.c 3-dog.c -o f Output:

$ valgrind ./f
==22840== Memcheck, a memory error detector
==22840== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==22840== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==22840== Command: ./f
==22840== 
My name is Poppy, and I am 3.5 :) - Woof!
==22840== 
==22840== HEAP SUMMARY:
==22840==     in use at exit: 0 bytes in 0 blocks
==22840==   total heap usage: 4 allocs, 4 frees, 1,059 bytes allocated
==22840== 
==22840== All heap blocks were freed -- no leaks are possible
==22840== 
==22840== For counts of detected and suppressed errors, rerun with: -v
==22840== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
$