Keyword typedef in C

The C program language provides a typedef keyword, which you can use to provide the type for a new name. Here is an example to define a BYTE entry for 1-byte numbers (like unsigned char).

The C program language provides a typedef keyword, which you can use to provide the type for a new name. Here is an example to define a BYTE entry for 1-byte numbers (like unsigned char).

 typedef unsigned char BYTE ;

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

 BYTE b1 , b2 ;

By convention, uppercase letters are used for these definitions to make it easier for users to remember, but you can use lower case letters as follows:

 typedef unsigned char byte ;

You can also use typedef to provide a name for the user defined data type. For example, you can use typedef with a structure to define a new data type and then use that data type to define structure variables directly as follows:

 #include #include typedef struct Books { char tieude [ 50 ]; char tacgia [ 50 ]; char chude [ 100 ]; int id ; } Book ; int main ( ) { Book book ; strcpy ( book . tieude , "Lap trinh C" ); strcpy ( book . tacgia , "Pham Van At" ); strcpy ( book . chude , "Ngon ngu lap trinh C" ); book . id = 1234567 ; printf ( "Tieu de: %sn" , book . tieude ); printf ( "Tac gia: %sn" , book . tacgia ); printf ( "Chu de: %sn" , book . chude ); printf ( "ID: %dn" , book . id ); printf ( "n===========================n" ); printf ( "QTM chuc cac ban hoc tot! n" ); return 0 ; }

Compiling and running the above C program will result:

Keyword typedef in C Picture 1 Keyword typedef in C Picture 1

typedef vs #define in C

#define is a directive in C which is also used to define aliases (abbreviations) for diverse data types similar to typedef but there are the following differences:

The typedef is limited to providing abbreviations for types only, while #define can be used to define nicknames for both values, as you can define 1 as ONE, .

The typedef translation is performed by the compiler, while the #define command is processed by the preprocessor.

Here is the simplest use of #define :

 #include #define TRUE 1 #define FALSE 0 int main ( ) { printf ( "Gia tri TRUE tuong duong: %dn" , TRUE ); printf ( "Gia tri FALSE tuong duong: %dn" , FALSE ); printf ( "n===========================n" ); printf ( "QTM chuc cac ban hoc tot! n" ); return 0 ; }

Compiling and running the above C program will result:

Keyword typedef in C Picture 2 Keyword typedef in C Picture 2