Question

So I have a char array in C…for example:

uchar arr[3] = { 0x34, 0x45, 0xFF }

I am looking for a fast way to add an integer to it (like its 0x3445FF) so for example if I add 2 to arr I get:

{ 0x34, 0x46, 0x01 }

Answer 1

The easiest and best way will be to convert to int, add, and then convert back. Also, you need to decide on the byte-order since it’s never clear.

This code assumes big-endian, i.e. the array initially holds the number 0x3445ff:

uint8_t arr[] = { 0x34, 0x45, 0xff };

uint32_t x = (arr[0] << 16) | (arr[1] << 8] | arr[2];

x += 2;

arr[0] = (x >> 16) & 0xff;
arr[1] = (x >> 8) & 0xff;
arr[2] = x & 0xff;