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:
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
Objective-C Typedef Example
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
typedef and #define
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.
Objective-C Online Test
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