Hello, I am sorry that I ask about this topic, even if it has been discussed so often, but I am really at a loss: First of all is there any website, link or docu (whatever) which lists some examples of what is legal (under strict aliasing) and what is not ? Let me try to explain what I understood: With the following variable definitions, unsigned int *ptr1; unsigned short *ptr2; "strict aliasing" means that the compiler is allowed to assume that "ptr1" and "ptr2" will NOT acceess to the same address (object). For optimization this means that if someone writes ptr2[0]=0x1111 ptr1[0]=0x22222222; then the compiler can assume that ptr2[0] still is "0x1111", because "ptr1" must not access to memory which is accessed through ptr2. Is this correct so far ? Now I am writing code for an embedded application (no OS). Because I know the architecture I want to do the following --- unsigned int value; unsigned char *ptr2; *((unsigned int *)ptr2) = value; --- The idea here is that you write a 32 bit value in big endian order to a byte (unsigned char) array. (The used architecture is big endian; I know that on some architectures that means that the pointer must point to an address which is aligned...) Now my understanding was that this code breaks strict aliasing rules, because I cast a "unsigned char *" to an "unsigned int *". BUT: The g++ 4.4.2 compiler does not complain with "-Wstrict-aliasing". Is the above statement OK or not ? Or is it, because "ptr2" is an "unsigned char *", that ptr2 is assumed to be able to alias anything ? (Because it is a char pointer). Does these "char pointer can alias anything" really only refer to "char *" or also to "unsigned char *". with best regards Ingo
