Storing allocated value to allocated array

Question

The code I have is this:

uint8_t* payload = (uint8_t*)malloc(payload_size);
uint8_t* payloads = (uint8_t*)malloc(payload_size * 100);

for(uint8_t i = 0; i < 100; i++ ){

create_payload(payload); //cannot modify 

//myapproach
payloads[i] = payload;

}

And this is not even compiling.

I'd like to store the payload values to the payloads array because the payload variable gets replaced at every iteration.

Is there a simple solution to this?

Answer 1

At first, payloads should point to pointers of uint8_t, not a uint8_t itself (Because you want to store pointers on this data)

Then, you using same buffer for every payload creation, so you filling payloads with pointer to the same data, you need to allocate new buffer for every payload

And, at last - size of resulting buffer will be

size of one entry *pointer* * count of entries

not a

size of one entry * count of entries

So resulting code will be:

uint8_t** payloads = (uint8_t**)malloc(sizeof(uint8_t*) * 100);
// uint8_t* payloads[100]; - Will also work

for(uint8_t i = 0; i < 100; i++ ){
    uint8_t* payload = (uint8_t*)malloc(payload_size);

    create_payload(payload); //cannot modify 

    payloads[i] = payload;
}

Or, if you wanted to have all payloads to be in same buffer, use malloc to copy payload to output:

uint8_t* payload = (uint8_t*)malloc(payload_size);
uint8_t* payloads = (uint8_t*)malloc(payload_size * 100);

for(uint8_t i = 0; i < 100; i++ ){

    create_payload(payload); //cannot modify 

    memcpy(payloads + i * payload_size, payload, payload_size);
}