Array members inside the structure variable - c

Question

I have a structure as follows
typedef struct s_CanMsg
{
uint32_t id;
uint16_t timestamp;
uint8_t data[8];
uint8_t dlc;
bool_t isExtended;
bool_t isRemote;
} s_CanMsg_t;
and I have a structure variable as follows
s_CanMsg_t CANEraseResponse;
Now I am trying to pass an array to the data member of the structure variable as follows:
CANEraseResponse.data[8] = {0x00, 0xFF, 0x00, 0x04, 0x02, 0x00, 0x00, 0x00};
This is showing syntax error and how can I pass the data to the structure variable with array member? Thanks in advance.

Answer 1

You can initialize the whole structure when you define the variable:
s_CanMsg_t CANEraseResponse = {
some_value_for_id,
some_value_for_timestamp,
{0x00, 0xFF, 0x00, 0x04, 0x02, 0x00, 0x00, 0x00},
some_value_for_dlc,
some_value_for_isExtended,
some_value_for_isRemote
};
You can also use a designator to explicitly initialize only the array member;
s_CanMsg_t CANEraseResponse = {
.data = {0x00, 0xFF, 0x00, 0x04, 0x02, 0x00, 0x00, 0x00}
};
Then all other members will be initialized to zero.
And of course you can define a temporary array and copy into the structure array:
static uint8_t data[8] = {0x00, 0xFF, 0x00, 0x04, 0x02, 0x00, 0x00, 0x00},
s_CanMsg_t CANEraseResponse;
memcpy(CANEraseResponse.data, data, sizeof data);
Lastly, if none of the ways above are acceptable, then the only remaining solution is to explicitly assign to each element of the array:
CANEraseResponse.data[0] = 0x00;
CANEraseResponse.data[1] = 0xFF;
CANEraseResponse.data[2] = 0x00;
CANEraseResponse.data[3] = 0x04;
CANEraseResponse.data[4] = 0x02;
CANEraseResponse.data[5] = 0x00;
CANEraseResponse.data[6] = 0x00;
CANEraseResponse.data[7] = 0x00;

Answer 2

The notation you are using can only be used to initialize an array. Once you declare your struct variable, you have moved past initialization. You can, however, do it with something called a "designated initializer" like so:
s_CanMsg_t CANEraseResponse = {.data= {0x00, 0xFF, 0x00, 0x04, 0x02, 0x00, 0x00, 0x00}};

Answer 3

CANEraseResponse.data[8] refers to the 9th element of the data member (as the array is zero based. Try removing the [8].
Edit/Clarification: removing the [8] will not solve your issue, but you should be aware that CANEraseResponse.data[8] points to a position outside of the data array.

Answer 4

You can't assign arrays directly in C. As well as the initialization techniques shown in other answers, you could use a compound literal and memmove() (or memcpy()):
memmove(CANEraseResponse.data, (uint8_t[]){ 0x00, 0xFF, 0x00, 0x04, 0x02, 0x00, 0x00, 0x00 }, sizeof(CANEraseResponse.data));