C tutorial

typedef in C

typedef <existing_name> <alias_name>

Lets take an example and see how typedef actually works.

typedef unsigned long ulong;

The above statement define a term ulong for an unsigned long datatype. Now this ulong identifier can be used to define unsigned long type variables.

ulong i, j;

Application of typedef

typedef can be used to give a name to user defined data type as well. Lets see its use with structures.

typedef struct
{
    type member1;
    type member2;
    type member3;
} type_name;

Here type_name represents the stucture definition associated with it. Now this type_name can be used to declare a variable of this stucture type.

type_name t1, t2;

Example of Structure definition using typedef

#include<stdio.h>
#include<string.h>
 
typedef struct employee
{
    char name[50];
    int salary;
}emp;
 
void main( )
{
    emp e1;
    printf("\nEnter Employee record:\n");
    printf("\nEmployee name:\t");
    scanf("%s", e1.name);
    printf("\nEnter Employee salary: \t");
    scanf("%d", &e1.salary);
    printf("\nstudent name is %s", e1.name);
    printf("\nroll is %d", e1.salary);
}

typedef and Pointers

typedef can be used to give an alias name to pointers also. Here we have a case in which use of typedef is beneficial during pointer declaration.

In Pointers * binds to the right and not on the left.

int* x, y;

By this declaration statement, we are actually declaring x as a pointer of type int, whereas y will be declared as a plain int variable.

typedef int* IntPtr;
IntPtr x, y, z;

But if we use typedef like we have used in the example above, we can declare any number of pointers in a single statement.

NOTE: If you do not have any prior knowledge of pointers, do study Pointers first.