------- Comment #10 from mikulas at artax dot karlin dot mff dot cuni dot cz 2009-07-07 18:07 ------- So you mean that that ->x operator is invalid and break the standard?
Anyway the standard means "if you write your code according to the standard => the code will run correctly", but the inverse implication doesn't apply. It is sometimes required to break the C standard. For example, you write "unsigned char *framebuffer = vga_getgraphmem();" and now you want to access the framebuffer. According to the standard, you could only do it by bytes. But that means one bus cycle to the videocard for every byte transfered. So people understand that common processors allow aligned accesses to 2, 4 or 8 bytes and that common videocards have their framebuffer base address aligned on same larger boundary --- and they simply cast the pointer to u_int32_t or u_int64_t and access the videoram faster. Each time you watch some video, remember those undefined memory accesses that are hapenning for you to get faster performance :) Another example --- the C standard says how it's not allowed to even produce a pointer that points before the allocated array or more than one entry after the last entry of the array and how it's not allowed to subtract two pointers from different arrays. It is perfectly rational --- unless you are writing the memory allocator itself! Then you inevitably must do some operations that are considered "undefined" by the standard. Regarding that int * to short * cast --- obviously, the code may run on some computer that has tagged memory and traps if access with invalid type is done. But common computers don't have tagged memory and the programmer should be allowed to do such casts if he understands the implications (for example, if its done only in arch-specific part of an operating system, it is perfectly legal). So there should be a method to silence the warning. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40665
