C Unions

Allowing you to look at each byte individually without casting a pointer and using pointer arithmetic:

union intParts parts;
parts.theInt = 5968145; // arbitrary number > 255 (1 byte)

printf("The int is %i\nThe bytes are [%i, %i, %i, %i]\n",
parts.theInt, parts.bytes[0], parts.bytes[1], parts.bytes[2], parts.bytes[3]);

// vs

int theInt = parts.theInt;
printf("The int is %i\nThe bytes are [%i, %i, %i, %i]\n",
theInt, *((char*)&theInt+0), *((char*)&theInt+1), *((char*)&theInt+2), *((char*)&theInt+3));

// or with array syntax which can be a tiny bit nicer sometimes

printf("The int is %i\nThe bytes are [%i, %i, %i, %i]\n",
    theInt, ((char*)&theInt)[0], ((char*)&theInt)[1], ((char*)&theInt)[2], ((char*)&theInt)[3]);

Combining this with a structure allows you to create a "tagged" union which can be used to store multiple different types, one at a time.

For example, you might have a "number" struct, but you don't want to use something like this: