Initializing structure array inside a structure array

Question

I have a question in initializing my structure array inside a structure array. for example if I have a code as below:

#include <stdio.h>

int main() {

typedef struct {
    int a;
    int b;
    int c;
} FIRST_T;

typedef struct {
    int x;
    int y;
    int z;
    FIRST_T *p;
} SECOND_T;

FIRST_T p1[]={{1,2,3},{3,4,5},{6,7,8}};
FIRST_T p2[]={{4,5,6},{7,8,9}};

SECOND_T my_second[]=
{
{1,2,3,p1},
{4,5,6,p2}
};

}

if I have to initialize my first array in second array intialization part itself, then how would I write my typedef of SECOND_T? like

SECOND_T my_second[]=
{
{1,2,3,{{1,2,3},{4,5,6},{7,8,9}}},
{4,5,6,{{1,1,1},{2,2,2}}}
};

then how should be my SECOND_T?

I am sure I can't define it as:

typedef struct {
    int x;
    int y;
    int z;
    FIRST_T p[]; //(I know its a blunder)
} SECOND_T;

Please help.

I am not getting your question perhaps if you are saying that you want to initialize a array inside another structure array that will not be possible. array has containing a address via that we can access element and you are initializing a array inside another so how first array element will access through second element. — Varun Chhangani, Jun 14 '13 at 13:01

Jinghao Shi · Answer 1 · 2012-03-23T11:36:26.670

1

I don't think you can do this, i.e, initialize the FIRST_T inside the initialization of SECOND_T, other than the first way you do it. Think about it, how can the compiler tell how many FIRST_T are there in SECOND_T? The problem here is, you can NOT define an array of flexible size struct statically.

edited Mar 23 '12 at 11:36

answered Mar 23 '12 at 06:24

Jinghao Shi

1,077
2
10
15

score 1 · Accepted Answer · answered Mar 23 '12 at 06:28

1

You can't define a type with unbounded array in C, you have to specify the dimension. So you either do:

typedef strut {
    int x;
    int y;
    int z;
    FIRST_T f[SOME_VALUE];
} SECOND_T;

and then initialize SOME_VALUE count of members always, or do it the way you did.

answered Mar 23 '12 at 06:28

littleadv

20,100
2
36
50

I'm not the downvoter but it's perfectly legal (since C99) to have flexible array members, so your comment is wrong – hroptatyr Mar 23 '12 at 11:43
@hroptatyr I believe you're wrong. You can declare unbounded array, but you cannot define its value in the way the OP wants. The default size of the unbounded array is 0, so you have to allocate memory before actually using it. I believe this question is of relevance: http://stackoverflow.com/questions/9324995/what-is-the-difference-between-square-bracket-arrays-and-pointer-arrays – littleadv Mar 23 '12 at 17:30

score 0 · Answer 3 · answered Mar 23 '12 at 07:15

you can't to do like that:

SECOND_T my_second[]=
{
{1,2,3,{{1,2,3},{4,5,6},{7,8,9}}},
{4,5,6,{{1,1,1},{2,2,2}}}
};

with

typedef struct {
int x;
int y;
int z;
FIRST_T p[]; //(I know its a blunder)

} SECOND_T;

becase the compiler don't know how to malloc memory for this struct. if you must do like this, you should define

typedef struct { int x,y,z; FIRST_T p[CONST_VALUE];}SECOND_T;

but I advise you use the first style that you write.

score 0 · Answer 4 · answered Mar 23 '12 at 07:16

I don't know if I completely capture the question that you have. If it is that you want to avoid to have to declare an auxiliary variable for the pointers in the structure you can use a compound literal as follows:

SECOND_T my_second[] = {
  {1,2,3, &(FIRST_T){{1,2,3},{3,4,5},{6,7,8}}},
  {4,5,6, &(FIRST_T){{4,5,6},{7,8,9}}}
};

You'd have a compiler that complies to C99 for that.

Initializing structure array inside a structure array

4 Answers4

Linked