structs in C with initial values [duplicate]

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; 

Errors:

$ gcc -o testIt test.c  test.c:7: error: expected ‘:’, ‘,’, ‘;’, ‘}’ or ‘__attribute__’ before ‘=’ token test.c: In function ‘main’: test.c:17: error: ‘struct <anonymous>’ has no member named ‘flag’ 

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

you can not do it in this way

Use the following instead

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

You can use macro to define and initialize your instances. this will make easiier to you each time you want to define new instance and initialize it.

typedef struct {    int id;    char* name; }employee;  #define INIT_EMPLOYEE(X) employee X = {.id = 0, .name ="none"} 

and in your code when you need to define new instance with employee type, you just call this macro like:

INIT_EMPLOYEE(emp);