Lesson 08 | Structures

Defining Structures With struct

Structures are defined with the struct keyword followed by the structure name. Inside the braces, member variables are declared but not initialized. The given code block defines a structure named Person with declared member variables name and age.

// `struct` keyword and structure name
struct Person{
  // uninitialized member variables
  char* name;
  int age;
};

Initializing Structures With struct

Structure data types are initialized using the struct keyword with the defined structure type followed by the name of the variable. The given code block shows two ways to initialize Person type structures named person1 and person2.

// `Person` structure declaration
struct Person{
  char* name;
  int age;
};

// designated initialization with member variable names
struct Person person1 = {.name = "Cosmo", .age = 36};

// implicit initialization following order of member variables
struct Person person2 = {"George", 29};

Custom Data Types With Structures

Structures allow the definition of custom data types that are used to represent complex data. Structure customization provides the flexibility to accurately model real-world data, giving you the ability to access and modify the data from a single defined variable.

Grouping Data Types With Structures

Structures can group different data types together into a single, user-defined type. This differs from arrays which can only group the same data type together into a single type. The given code block defines a structure named Person with different basic data types as member variables.

// `Person` structure definition
struct Person{
  // member variables that vary in type
  char* name;
  int age;
  char middleInitial;
};

Accessing Member Variables With Dot Notation

Initialized structure member variables can be accessed with the dot (.) operator. The given code block initializes a Person type named person1 and accesses the name member variable within a printf() statement.

// `Person` structure declaration
struct Person{
  // member variables
  char* name;
  int age;
  char middleInitial;
};

// initialization of `person1`
struct Person person1 = {.name = "George", .age = 28, .middleInitial = "C"};

// accessing `name` in `person1`
printf("My name is %s", person1.name);
// OUTPUT: My name is George

Structure Member Variables

The variables defined within a structure are known as member variables. The given code block defined a structure named Person with member variables name of type char*, and age of type int.

// Person structure declaration
struct Person{
  // member variables
  char* name;
  int age;
};

Structure Type Pointers

Pointers to a structure can be defined using the struct keyword, the structure type, and the pointer (*) symbol. The memory address of an initialized structure can be accessed using the symbol (&). The given code block defines a pointer to a Person data type named person1.

// Person structure declaration
struct Person{
  // member variables
  char* name;
  int age;
};

// person1 initialization
struct Person person1 = {"George", 28};

// person1Pointer initializated to the memory address of person1
struct Person* person1Pointer = &person1;

Accessing Member Variables With Arrow Notiation

Member variables of a structure can be accessed using a pointer with arrow (->) notation. The given code block initializes a Person pointer type named person1Pointer. Inside the printf() statement, the name member variable of person1 is accessed using arrow (->) notation.

// `Person` structure declaration
struct Person{
  // member variables
  char* name;
  int age;
};

// `person1` intialization
struct Person person1 = {"Jerry", 29};

// `person1Pointer` intialization to memory address to `person1`
struct Person* person1Pointer = &person1;

// accessing `name` through `person1Pointer`
printf("My name is %s", person1Pointer->name);
// OUTPUT: My name is Jerry

Passing Structures To Functions

Structures can be used as parameters of functions by using the struct keyword followed by the structure name in the function definition. The given code block defines a function signature named myFunc() with a Person parameter named person1.

// Person structure declaration
struct Person{
  // member variables
  char* name;
  int age;
};

// declaring Person type parameter
void myFunc(struct Person person1);

Passing Structure Pointers To Functions

Structure pointers can be paramters of functions by using the struct keyword, the structure name, and the pointer symbol (*) in the function definition. The given code block defines a function signature named myFunc() with a Person pointer parameter named person1 pointer.