I have been looking at c pointer to array of structs , and trying to apply it to my example.
I arrived at this code snippet, which compiles fine:
#include <stdio.h>
enum test_e {
eONE,
eTWO,
eTHREE,
};
typedef enum test_e test_t;
#define NUMITEMS 12
extern test_t my_arr[NUMITEMS];
test_t (*my_arr_ptr)[NUMITEMS];
test_t my_arr[NUMITEMS] = { 0 };
int main()
{
my_arr_ptr = &my_arr;
printf("Hello World %p\n", my_arr_ptr);
return 0;
}
In the above snippet, we have an assignment of my_arr_ptr variable, to the address of my_arr variable (using the "address of " operator, ampersand &).
However, what I would like to do is to initialize my_arr_ptr variable to the address of my_arr variable - which I'd think is possible, given that after the line test_t my_arr[NUMITEMS] = { 0 }; the compiler should "know" an address and size of my_arr.
However, if I try this:
#include <stdio.h>
enum test_e {
eONE,
eTWO,
eTHREE,
};
typedef enum test_e test_t;
#define NUMITEMS 12
extern test_t my_arr[NUMITEMS];
test_t (*my_arr_ptr)[NUMITEMS];
test_t my_arr[NUMITEMS] = { 0 };
my_arr_ptr = &my_arr;
int main()
{
//my_arr_ptr = &my_arr;
printf("Hello World %p\n", my_arr_ptr);
return 0;
}
... this fails with:
Compilation failed due to following error(s).
main.c:25:1: warning: data definition has no type or storage class
25 | my_arr_ptr = &my_arr;
| ^~~~~~~~~~
main.c:25:1: warning: type defaults to ‘int’ in declaration of ‘my_arr_ptr’ [-Wimplicit-int]
main.c:25:1: error: conflicting types for ‘my_arr_ptr’; have ‘int’
main.c:21:10: note: previous declaration of ‘my_arr_ptr’ with type ‘test_t (*)[12]’ {aka ‘enum test_e (*)[12]’}
21 | test_t (*my_arr_ptr)[NUMITEMS];
| ^~~~~~~~~~
main.c:25:14: warning: initialization of ‘int’ from ‘test_t (*)[12]’ {aka ‘enum test_e (*)[12]’} makes integer from pointer without a cast [-Wint-conversion]
25 | my_arr_ptr = &my_arr;
| ^
main.c:25:14: error: initializer element is not computable at load time
main.c: In function ‘main’:
main.c:30:26: warning: format ‘%p’ expects argument of type ‘void *’, but argument 2 has type ‘int’ [-Wformat=]
30 | printf("Hello World %p\n", my_arr_ptr);
| ~^ ~~~~~~~~~~
| | |
| | int
| void *
| %d
As far as I can see, "warning: data definition has no type or storage class" occurs:
because you can't execute code outside functions
(Why am I getting this error: "data definition has no type or storage class"?)
So, then, is the getting of "address of" considered "code" in C, so I cannot use it outside functions?
If so, how come I can use "address of" operator "outside functions" in the snippet below, which also compiles fine?:
#include <stdio.h>
void func_one(void) {
printf("func_one\n");
}
void func_two(void) {
printf("func_two\n");
}
void* funcs_arr[2] = { &func_one, &func_two };
int main()
{
printf("Hello World %p\n", funcs_arr[0]);
return 0;
}
