TYPEDEF

TYPEDEF

The C programming language provides a keyword called typedef, which you can
use to give a type, a new name. Following is an example to define a
term BYTE for one-byte numbers:

typedef unsigned char BYTE;

After this type definition, the identifier BYTE can be used as an abbreviation for
the type unsigned char, for example:

BYTE b1, b2;

By convention, uppercase letters are used for these definitions to remind the
user that the type name is really a symbolic abbreviation, but you can use
lowercase, as follows:

typedef unsigned char byte;

You can use typedef to give a name to your user-defined data types as well. For
example, you can use typedef with structure to define a new data type and then
use that data type to define structure variables directly as follows:

#include <stdio.h> #include <string.h> typedef struct Books { char title[50]; char author[50]; char subject[100]; int book_id; } Book; int main( ) { Book book; strcpy( book.title, "C Programming"); strcpy( book.author, "Nuha Ali"); strcpy( book.subject, "C Programming Tutorial"); book.book_id = 6495407; printf( "Book title : %s\n", book.title); printf( "Book author : %s\n", book.author); printf( "Book subject : %s\n", book.subject); printf( "Book book_id : %d\n", book.book_id); return 0; }

When the above code is compiled and executed, it produces the following result:

Book title : C Programming Book author : Nuha Ali Book subject : C Programming Tutorial Book book_id : 6495407

typedef  vs #define

#define is a C-directive which is also used to define the aliases for various data
types similar to typedef but with the following differences:

· typedef is limited to giving symbolic names to types only,
whereas #define can be used to define alias for values as well, e.g., you
can define 1 as ONE, etc.

· typedef interpretation is performed by the compiler whereas #define
statements are processed by the preprocessor.

The following example shows how to use #define in a program:

#include <stdio.h> #define TRUE 1 #define FALSE 0 int main( ) { printf( "Value of TRUE : %d\n", TRUE); printf( "Value of FALSE : %d\n", FALSE); return 0; }

When the above code is compiled and executed, it produces the following result:

Value of TRUE : 1 Value of FALSE : 0