How to statically inialize an array of structures? - c

Question

struct A{
int a; int b;
};
static const struct A a = {.a1 = 1, .a2 = 42};
struct B{
struct A[666][510]
};
static const struct B b;
I would like to initialize b with copies of a. However, I cannot touch static const things with memcpy(). And I need b to be static const, because that way it gets put into flash and not ram memory.
How do I make this work. The compiler is arm-none-eabi-gcc with -std=c89, I think.

Answer 1

You can try this, though it works specifically for the dimensions that you specify (666 x 510):
#define X001 {1,42}
#define X002 X001,X001
#define X004 X002,X002
#define X008 X004,X004
#define X016 X008,X008
#define X032 X016,X016
#define X064 X032,X032
#define X128 X064,X064
#define X256 X128,X128
#define Y001 {X256,X128,X064,X032,X016,X008,X004,X002}
#define Y002 Y001,Y001
#define Y004 Y002,Y002
#define Y008 Y004,Y004
#define Y016 Y008,Y008
#define Y032 Y016,Y016
#define Y064 Y032,Y032
#define Y128 Y064,Y064
#define Y256 Y128,Y128
#define Y512 Y256,Y256
static const struct A a = X001;
static const struct B b = {{Y512,Y128,Y016,Y008,Y002}};

Answer 2

I recommend that you put these arrays in a separate module in order to achieve encapsulation. Then inside that module you do not need to make B a const but make it static instead.
Any access to this data must be done via getters and setters like this:
mydata.h
#define BA_SIZE 666
struct A{
int a; int b;
};
struct B{
struct A stuff[BA_SIZE];
};
void init(void);
struct A * getB(unsigned int i);
void setB(unsigned int i, struct A element);
mydata.c:
#include "mydata.h"
static const struct A a = {.a = 1, .b = 42};
static struct B b;
void init(void)
{
int i;
for(i=0; i&ltBA_SIZE; i++) {
b.stuff[i] = a;
}
}
struct A * getB(unsigned int i)
{
return(&b.stuff[i]);
}
void setB(unsigned int i, struct A element)
{
if (i &gt BA_SIZE) { return; }
b.stuff[i].a = element.a;
b.stuff[i].b = element.b;
}
main.c:
#include &ltstdio.h&gt
#include "mydata.h"
int main(void)
{
init();
unsigned int num=1;
struct A * something = getB(num);
printf("element [%u] a=%i b=%i \n", num, something-&gta, something-&gtb);
return(0);
}

Answer 3

On linux this complies with gcc -std=c89 (don't know about arm cross compiler)
typedef struct A{
int a; int b;
} TA;
typedef struct ARR3 {
TA a[3];
} TARR3;
typedef struct ARR33 {
TARR3 b[3];
} TARR33;
static const TA a = {.a = 1, .b = 42};
TARR33 aa = {
.b[0] = { .a[0] = {.a = 1, .b = 1}, .a[1] = {.a = 2, .b = 2}, .a[2] = {.a = 3, .b = 3} },
.b[1] = { .a[0] = {.a = 4, .b = 4}, .a[1] = {.a = 5, .b = 5}, .a[2] = {.a = 1, .b = 2} },
.b[2] = { .a[0] = {.a = 1, .b = 1}, .a[1] = {.a = 1, .b = 2}, .a[2] = {.a = 1, .b = 2} }
};
main()
{
return 0;
}