Initialise global array of arrays of structs

Question

I am declaring an array of struct this way :

struct struct_name tab1[6] ={ {"1487" ,0.144}, {"148",2.1},    {"45",0.01}, {"12475847",0.52}, {"46",1.4}, {"0",5} };
struct struct_name tab2[7] = { {"1" ,0.9}, {"76",5.1},{"46",0.17},{"4625",0.0},{"46252",1.57},{"12",1.5},{"5",1.2} };

This works fine.

Now I need to make tab1 and tab2 in one array global_tab and still initialize data this way but so far I haven't been able to do so. I tried dynamic allocation like this

global_tab = malloc(2 * sizeof(struct struct_name *));
global_tab[0] = malloc(100 * sizeof(struct struct_name));
global_tab[0] = { {"1487" ,0.144}, {"148",2.1}, {"45",0.01}, {"12475847",0.52}, {"46",1.4}, {"0",5} };

But I get this error

error: expected expression before ‘{’ token
  global_tab[0] ={ {"1487" ,0.144}, {"148",2.1}, {"45",0.01}, {"12475847",0.52}, {"46",1.4}, {"0",5} };

I want to be able to do initialize global_tab[0] the same way I did with tab1

Side note: global_tab[0] = something then global_tab[0] = something else means that the first assignment is pretty much useless. It's like doing int i = 5; i = 6;. — barak manos
– barak manos, Commented Jul 25, 2015 at 11:23
IIRC, C initialiser lists are only available for static and auto storage duration? — Martin James
– Martin James, Commented Jul 25, 2015 at 11:25

Sergey Kalinichenko · Accepted Answer · 2015-07-25 11:24:21Z

3

C does not provide array aggregate assignment. The curly brace construct is available only in initialization expressions^*. If you would like to place specific data into a dynamically allocated block, you could make a static variable with the data, and use memcpy, like this:

static struct struct_name tmp0[] ={ {"1487" ,0.144}, {"148",2.1},    {"45",0.01}, {"12475847",0.52}, {"46",1.4}, {"0",5} };
global_tab[0] = malloc(sizeof(tmp0));
memcpy(tmp0, global_tab[0], sizeof(tmp0));

^* Some compilers provide struct and array aggregates as an extension, but using this feature makes your code non-portable.

answered Jul 25, 2015 at 11:24

Sergey Kalinichenko

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Yu Hao · Accepted Answer · 2015-07-25 11:21:39Z

2

You are confused about initialization and assignment. These operations are different, despite that they both use =:

int m = 42;  // initialization
int n;
n = 42;  // assignment

The code in error is similar:

global_tab[0] = { {"1487" ,0.144}, {"148",2.1}, {"45",0.01}, {"12475847",0.52}, {"46",1.4}, {"0",5} };

This is assignment, you can't use the initialization syntax. The C99 compound literal is perhaps what you want.

answered Jul 25, 2015 at 11:21

Yu Hao

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1 Comment

Peter Cordes Over a year ago

If global_tab wasn't dynamically allocated, it could be initialized.

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