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Structure and typedef

Structure and typedef

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milam
·

4 min read

C allows the creation of a user-defined variable. A situation can arise where one needs to store different but logically related values under a single variable. An example is product information. It can consist of the following attributes

  • id (int)
  • name (string)
  • price (float)

A structure/struct allows creating a user-defined data type (Product) consisting of different data types (float, string, price) under a single type.

To create a structure, a struct keyword is used and the consisting different datatypes that it holds are called members.

Syntax 

struct struct_name {
   datatype member1;
   dataype member2;
   …
};

Creating the structure of the product example would be -

struct Product
{
   int id;
   char *name;
   float price;
};

Datatype Product has been created and a variable can be declared in the following two ways. 

struct Product p;

whereby Product = datatype and p = variable. Or

struct Product
{
   int id;
   char *name;
   float price;
} p;

Initializing and Accessing Structures

Structures cannot be initialized upon declaration but instead once the struct has been created. In a process known as designated initialization, structure members can be initialized in no particular through using a dot operator to access the members.

struct Product p = {.price = 89.45, .id = 1234, .name = "Watch"}
  • id (int)
  • name (string)
  • price (float)

A structure/struct allows creating your data type consisting of different data types under a single name

own_datatype{
//contains different types of data types
}

To create a structure, a struct keyword is used and the declared datatypes are called members.

Syntax 

struct struct_name {
   datatype member1;
   dataype member2;
   …
};

Creating the structure of the product example would be 

struct Product
{
   int id;
   char *name;
   float price;
};

Datatype Product has been created and a variable can be declared in the following two ways. 

struct Product p;

whereby Product = datatype and p = variable. Or

struct Product
{
   int id;
   char *name;
   float price;
} p;

Declaring and Initializing

Structures cannot be initialized upon declaration but instead once the struct has been created. The elements can be initialized in no particular order through a process known as designated initialization. The dot operator (.) is used to access the members and set values. 

struct Product p = {.id = 1234, .name = "John", .price = 21.4}

Product p variable is declared and initialized.

Accessing Members

A struct variable is used to access the members of the struct. Elements can be accessed by

  • using the dot operator (.) 
    struct Product p;
p.name = "John";
  • using a pointer
    struct Product *ptr;
ptr -> name = "John";

Example in program

#include <stdio.h>

struct Product
{
   int id;
   char *name;
   float price;
};

int main()
{
    struct Product p;
    p.id = 1204;
    p.name = "Watch";
    p.price = 24.56;
    printf("id: %d name: %s price: %.2f \n", p.id, p.name, p.price);
    return 0;
}

Using structure in functions

Functions can return a struct type and contain struct variables on its parameters.

  • Function that returns a struct type ``` #include

struct Product { int id; char *name; float price; };

struct Product funcStruct() { struct Product p; p.name = "Jane"; p.id = 1204; p.price = 24.56; return p; }; int main() { struct Product p;

p = funcStruct();
printf("id: %d name: %s price: %.2f \n", p.id, p.name, p.price);

func(p);
return 0;

}

  • Function that uses struct type as arguments 
#include <stdio.h>
#include <stdlib.h>

struct Product
{
   int id;
   char *name;
   float price;
};

void func(struct Product p)## 
{
p.name = "Jane";
    p.id = 1204;
    p.price = 24.56;
    printf("id: %d name: %s price: %.2f \n", p.id, p.name, p.price);
}

int main()
{
    struct Product p;
    func(p);
    return 0;
}

Typedef

This is a keyword that allows creating a new name for a datatype.

Syntax

typedef data_type new_name;

The new name can be used to create variables instead of using datatype. 

typedef char myChar;
myChar a = 'g';
printf("%c", a);

Typedef is convenient to use with structures. Instead of rewriting "struct Product p" to use, a datatype of type struct can be generated and used instead to declare struct variables.

Example in a program

#include <stdio.h>
#include <stdlib.h>

typedef struct Product
{
   char *name;
   float price;
} product;
int main() 
{
product p[] =
    {
         {"Watch", 2.45},
         {"Tshirt", 1.45},
         {"Shoes", 4.45},

     };
     int i;
    for (i=0; i < 3; i++)
    {
        printf("Name: %s Price: %.2f \n", p[i].name, p[i].price);
    }
return 0;
}

This is how to create struct and typedef and how to use both concepts together. I hope this write-up has been of help to you.

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