Typedef is a keyword, used in giving a new name for a data type in Objective-C.
Here is an example to define a term BYTE for one-byte numbers:
typedef unsigned char BYTE;
After this type definition, the identifier BYTE now can be used as an abbreviation for the type unsigned char. Here is an example to use BYTE as unsigned char:
BYTE bt1, bt2;
You can also use the keyword typedef to give a name to the user-defined data type in Objective-C also. Below is an example program illustrates this concept in Objective-C
You are free to use typedef with structure to define a new data type and then use that data type to define the structure variables directly like this:
/* Objective-C Typedef - Example Program */
#import <Foundation/Foundation.h>
typedef struct BOOKS
{
NSString *title;
NSString *author;
NSString *subject;
int bookid;
}Book;
int main()
{
Book book;
book.title = @"Objective-C Typedef Tutorial";
book.author = @"codescracker";
book.subject = @"Objective-C Programming Tutorial";
book.book_id = 100;
NSLog( @"Book Title = %@\n", book.title);
NSLog( @"Book Author = %@\n", book.author);
NSLog( @"Book Subject = %@\n", book.subject);
NSLog( @"Book ID = %d\n", book.bookid);
return 0;
}
When the above code is compile and executed, it will produce the following result:
2014-10-03 13:18:37.932 demo[31183] Book Title = Objective-C Typedef Tutorial 2014-10-03 13:18:37.932 demo[31183] Book Author = codescracker 2014-10-03 13:18:37.932 demo[31183] Book Subject = Objective-C Programming Tutorial 2014-10-03 13:18:37.932 demo[31183] Book ID = 100
The #define is an Objective-C preprocessor directive, which is also used to define the aliases for the various data types similar to the typedef but with these differences:
| typedef | #define |
|---|---|
| The typedef interpretation is performed by the compiler | The #define statements are processed by the Objective-C preprocessor |
| The typedef is limited to giving symbolic names to types only | The #define can be used to define alias for the values as well. For example, you can defined 3 as THREE |
To learn more about #define, then refer Objective-C Preprocessors.
© Copyright 2021. All Rights Reserved.