在C中将字节数据从一个数组传输到另一个数组

Question

So I have two dynamically allocated integer variables (A and B). Each of them is of size 12 which makes each of 48 bytes. I want to transfer data from one to another in bytes basis and want to complete the transfer in 32 rounds (loops). I would describe below what I am trying to achieve:

• Round 1 : First 2 Bytes (bytes 1 and 2) of array A to Array B
• Round 2 : Next 2 Bytes (bytes 3 and 4) of array A to array B

Goes on transferring 2 Bytes up to round 16. In round 16, 31st and 32nd bytes would be transferred.

Then from round 17 to 32 transfer rate would be 1 Bytes/ Round, ie

• Round 17 : 33rd Byte from A to B
• Round 18 : 34th Byte from A to B

......

• Round 32 : 48th Byte from A to B

Below I have attached a code snippet :

int *A,*B;

    A = (int *)malloc(12*sizeof(int));
    B = (int *)malloc(12*sizeof(int));

    for(int i= 0;i<12;i++)
     A[i] = i+1;

    for(int i=0;i<32;i++){

      if(i<16)
        //Transfer two byte from A to B in first 16 rounds, 2 bytes/round
      else
       // transfer 1 byte from A to B in next 16 rounds, 1 byte/round
    }

    free(A);
    free(B);

I can understand that this might be achieved using memcpy but I am confused in performing the address calculation. I am not sure if I am taking the correct approach. Please let me know if I am clear enough in my explanation. Any help would be very much appreciated. Thank you.

Answer 1

You need to use char* pointers to access individual bytes of the buffers, and uint16_t* for the 2-byte blocks.

char *cA = (char *)A;
char *cB = (char *)B;

uint16_t *iA = (uint16_t *)A;
uint16_t *iB = (uint16_t *)B;

for(int i=0;i<32;i++){

    if(i<16) {
        //Transfer two byte from A to B in first 16 rounds, 2 bytes/round
        iB[i] = iA[i];
    }
    else {
        // transfer 1 byte from A to B in next 16 rounds, 1 byte/round
        cB[16 + i] = cA[16 + i];
    }
 }