static member(2d array) of structure (2d array) in C - c

Question

I got a question regarding to static member of structure
Here is the scenario:
Need 2d array variable to retain its values even after exited from the function in another C files. Subsequent call from main()-in another C file, to the function will use that last value and continue to do calculation to produce and update new values(retained also). So, I I think I need to use static for that array.
The 2D array is member of an 2D structure. I need 2D structure for identity purposes for the 2d array. Lets say I got identity[row][column] with member[5][5], I need statically define the member throughout the call from main(). But static for structure member is not allowed in C as I notice.
code i am trying on:
//in function.h
#define row 2
#define column 5
int function(int rowNUM);
//in function.c
int function(int rowNUM)
{
typedef struct {
static int member[5][5];
int y[5][5];
int forg;
} mystruct;
mystruct identity[row][column];// declare the identity as structure array
int columnNUM;
int c;
int d;
//----try to initialize member to 1
for (columnNUM=0;columnNUM<column;columnNUM++)
{
for (c=0;c<5;c++)
{
for(d=0;d<5;d++){
identity[rowNUM][columnNUM].member[c][d]=1;
}
}
}
//----try to update member--- The values should retain for subsequent call from main
for (columnNUM=0;columnNUM<column;columnNUM++)
{
for (c=0;c<5;c++)
{
for(d=0;d<5;d++){
identity[rowNUM][columnNUM].member[c][d]=1+identity[rowNUM][columnNUM].member[c][d]; // to update member new value
}
}
}
}
// in main.c
main()
{
function(1);
function(2);// member here is in different identity from function (1)
function(1);//member should retain its value from function(1)
function(2);//member should retain its value from function(2)
}
Any other suggestion is welcomed if this is not the way to achieve the goal.
I am quite new in programing Please help me on this.

Answer 1

You have defined a 2d array of structs, which is really hard to statically initialize because each struct contains matrices of ints. Also, you can't have only a member of a struct static, the whole structure has to be defined static.
The easiest way I can think of doing what you want is defining an static matrix of mystructs and a helper variable to initialize it just on the first call, ie,
//in function.c
#include <stdbool.h>
int function(int rowNUM)
{
typedef struct {
int member[5][5];
int y[5][5];
int forg;
} mystruct;
// helper flag
static bool first_call = true;
// this is a matrix of (row x cols) mystructs
static mystruct identity[row][col];
if (first_call) {
/* initialize the matrix however you want
BUT remember to set first_call to false!
*/
first_call = false;
}
// rest of function ...
}
If you don't want to keep the values of the y and forg members (what does forg stand for? is it a typo?), you should split the struct in two, but I can't see why would you want to keep some values of the struct and discard others unless they are temporal variables.
If y and forg are temporal varaibles, you should definitely split your struct definition in two.
Another way of doing that is passing the pointer to the matrix as a parameter to your function, so you can maintain state without using a static variable
int function(int rowNUM, mystruct **identity)
But note that, although most of the times arrays decay to pointers (you can find more information in similar questions to this one), they are not the same thing.

Answer 2

If you only want a member of the struct to be static, your best option will be to make a static type in the function, which in your case would be a static 2D array, and do the assignment to the [stack] structure when the function is called.
Eg:
.. function(...)
{
static int b[2][2]
typedef struct { int a[2][2] } struct1;
struct1 x[2][2];
x->a = b;
}

Answer 3

void function(int rowNUM){
int c;
int d;
int columnNUM;
typedef struct {
int member[3][3];
}mystruct;
mystruct identity[ROW][COLUMN];
static bool first_call = true;
if (first_call) {
// INTIALIZE each element of member array to 1
for (columnNUM=0;columnNUM<COLUMN;columnNUM++)//total cell
{
for (c=0;c<3;c++)
{
for(d=0;d<3;d++){
identity[rowNUM][columnNUM].member[c][d]=1;
//printf("identity[%d][%d].member[%d][%d]=%d\n",rowNUM,columnNUM,c,d,identity[rowNUM][columnNUM].member[c][d]);
}
}
}
first_call = false;
}
identity[0][0].member[0][0]=identity[0][0].member[0][0]+3;
printf("%d\n", identity[0][0].member[0][0]);
identity[0][0].member[0][1]=identity[0][0].member[0][1]+1;
printf("%d\n", identity[0][0].member[0][1]);
}
The above code produce:
first call= 4 2 second call= 7 3 third call= 10 4
Work perfectly fine,nice. But it works fine either I declare
mystruct identity[ROW][COLUMN];
or
static mystruct identity[ROW][COLUMN];
Does it mean I dont need to declare static at all?