C – Typedef – Learn C, C++ Programming

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Typedef is a keyword that is used to give a new symbolic name for the existing name in a C program. This is same like defining alias for the commands.
Consider the below structure.

struct student
{
int mark [2];
char name [10];
float average;
}

Variable for the above structure can be declared in two ways.

1^st way :

struct student record; /* for normal variable */
struct student *record; /* for pointer variable */

2^nd way :

typedef struct student status;

When we use “typedef” keyword before struct <tag_name> like above, after that we can simply use type definition “status” in the C program to declare structure variable.
Now, structure variable declaration will be, “status record”.
This is equal to “struct student record”. Type definition for “struct student” is status. i.e. status = “struct student”

An alternative way for structure declaration using typedef in C:

typedef struct student
{
int mark [2];
char name [10];
float average;
} status;

To declare structure variable, we can use the below statements.

status record1; /* record 1 is structure variable */
status record2; /* record 2 is structure variable */

Example program for C typedef:

// Structure using typedef:

#include <stdio.h>
#include <string.h>

typedef struct student 
{
  int id;
  char name[20];
  float percentage;
} status;

int main() 
{
  status record;
  record.id=1;
  strcpy(record.name, "Raju");
  record.percentage = 86.5;
  printf(" Id is: %d n", record.id);
  printf(" Name is: %s n", record.name);
  printf(" Percentage is: %f n", record.percentage);
  return 0;
}

Output:

Id is: 1
Name is: Raju
Percentage is: 86.500000

Typedef can be used to simplify the real commands as per our need.
For example, consider below statement.

typedef long long int LLI;

In above statement, LLI is the type definition for the real C command “long long int”. We can use type definition LLI instead of using full command “long long int” in a C program once it is defined.

Another example program for C typedef:

#include <stdio.h>
#include <limits.h>

int main()
{
   typedef long long int LLI;

   printf("Storage size for long long int data " 
          "type  : %ld n", sizeof(LLI));

   return 0;
}

Output:

Storage size for long long int data type : 8

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