Re: Aliasing: reliable code or not?

[Ian Lance Taylor <iant at google dot com>]

Andrew Pinski <pinskia@physics.uc.edu> writes:

> Here is how I would write it so you can get the best results:
> 
> char *foo(char *buf)
> {
>   short temp;
>   int temp1;
>   *buf++=42;
>   temp = 0xfeed;
>   memcpy(buf, &temp, sizeof(temp));
>   buf+=sizeof(temp);
>   temp1 = 0x12345678;
>   memcpy(buf, &temp1, sizeof(temp1));
>   buf+=sizeof(temp1);
>   temp1 = 0x12345678;
>   memcpy(buf, &temp1, sizeof(temp1));
>   buf+=sizeof(temp1);
>   return buf;
> }

Or you can use constructor expressions to make this slightly more
elegant, though I retain the assumptions about type sizes:

char *foo1(char* buf){
  memcpy(buf, (char[]) { 42 }, 1);
  buf += 1;
  memcpy(buf, (short[]) { 0xfeed }, 2);
  buf += 2;
  memcpy(buf, (int[]) { 0x12345678 }, 4);
  buf += 4;
  memcpy(buf, (int[]) { 0x12345678 }, 4);
  buf += 4;
  return buf;
}

Ian