C语言中的结构声明

Question

Whether following structure declaration is right.

typedef struct  { 
int roll; 
int  age ; 
} class[10];

When I do like this , compiler does not say any error. But, when I assign class[0].age=10,
am getting error. So here class[0] struct variable or structure name..

Thanks

Answer 1

You are defining a type class which is an array of ten structs. To use this type you have to instatiate a variable of that type:

class x;
x[0].age = 10;

Maybe a slightly cleaner way would be to have two separate typedefs:

typedef struct { int roll; int  age; } foo_unit;
typedef foo_unit foo_array[10];

foo_array x;     /* now an array of 10 foo_units. */
foo_unit  y[10]; /* same thing */

Answer 2

I think what you want to do is

struct { 
  int roll; 
  int  age ; 
} class[10];

In your current code, class is defined as a type, because of the typedef. It's fine to define types this way, but you have to declare a variable afterwards:

typedef struct { 
  int roll; 
  int  age ; 
} class_type[10];

class_type class;

Answer 3

By making this typedef, you define a type. So in order to get your desired effect you should do the following:

   class myclass;
   myclass[0].age = 1;

Answer 4

class is the type name of an array of 10 elements each equal to the struct you define.

You should instantiate the type:

class classObject;

You have been possibly mislead by the basic syntax for declaring a struct:

struct class { 
   int roll; 
   int  age ; 
} class[10];

this declaration will also define a variable, array of 10 struct class .

By prefixing it with typedef you are changing the way the declaration works, and defining instead the type name instead of an instance of the struct.