Using typedef

[juvelover]

Hi all. just want to know for what and why we use "typedef" ?
i just doing some homework and I found it in example below
we have one struct named " Student" and there was one function like that

  typedef Student * ptrType;

and here the srudent struct :

  struct Student
{
   int id;
   char name[30];
   char address[30];
   char city[30];
   char state[30];
   char zip[30];
   float gpa;
   Box * next;
};

thanks

[nvrmnd]

typedef is used to define an alias for an already existing type,
it's format is :

typedef <data_type> <alias> ;

say i want to define an alias for an unsigned int, i'll do it as follows :

typedef unsigned uint_t;

since it is now an alias for unsigned int, you can happily declare a variable using uint_t, and you can use it for another typedef also !

uint_t foo; // an unsigned integer
unsigned var; // same as the above

// now, this is something different,
// we will define an alias to a pointer to an unsigned int :
typedef uint_t* pUint_t; // pUint_t is an alias for a pointer to an unsigned
// same as
typedef unsigned* pUint_t;

// now we can declare a pointer to unsigned using pUint_t :
pUint_t pointer_to_unsigned; // a pointer to unsigned
// it is same as :
unsigned* pointer_to_unsigned

BTW, i use _t suffix to denote that it is a typedef, and a p prefix to denote that it is a pointer

~~~

so in your code, ptrType is an alias for a pointer to a Student.

typedef Student* ptrStudent;

ptrStudent student_; // remember that student_ is a pointer, NOT an object of Student
student_ = new sizeof( Student );
student_->id = 1234;
strcpy( student_->name, "John" );
// etc...
delete[] student_;

i hope this helps !