default value for struct member in C

Question

Is it possible to set default values for some struct member? I tried the following but, it\'d cause syntax error:

typedef struct
{
  int flag = 3;
} MyStruct         


        

Answer 1

Structure is a data type. You don't give values to a data type. You give values to instances/objects of data types.
So no this is not possible in C.

Instead you can write a function which does the initialization for structure instance.

Alternatively, You could do:

struct MyStruct_s 
{
    int id;
} MyStruct_default = {3};

typedef struct MyStruct_s MyStruct;

And then always initialize your new instances as:

MyStruct mInstance = MyStruct_default;

Answer 2

If you are using gcc you can give designated initializers in object creation.

typedef struct
{
   int id=0;
   char* name="none";
}employee;

employee e = 
{
 .id = 0;
 .name = "none";
};

Or , simply use like array initialization.

employee e = {0 , "none"};

Answer 3

An initialization function to a struct is a good way to grant it default values:

Mystruct s;
Mystruct_init(&s);

Or even shorter:

Mystruct s = Mystruct_init();  // this time init returns a struct

Answer 4

I think the following way you can do it,

typedef struct
{
  int flag : 3;
} MyStruct;