Thread: Overflow check

What kind of assignment? Regular old x=3? [edit] If so you could compare the value casted to the smaller type with the value.

Code:

if(10000000000L != (short)10000000000L) overflow();

[/edit]

Are you adding something to a variable, x+=3? If so you could try something like this:

Code:

#include <limits.h>

short x = SHRT_MAX;

if(1 + (long)x > SHRT_MAX) overflow();
x += 1;

If there is such a thing as a "Status register" it isn't part of the ANSI standard.

[edit=2] This is integer overflow, right? http://en.wikipedia.org/wiki/Integer_overflow [/edit]

It can be done without casting

Code:

int x = 6;
if(x> INT_MAX - 3) overflow();
else x += 3;

I knew that . . .

But all the examples you've been given check for overflow before you assign the value. If you've already gone ahead and assigned the value, there's no way to tell if the integer overflowed (unless you have access to the original value, in which case you could check for overflow before the assignment anyway).

The constants in limits.h are very useful for this kind of thing.

Well, that is definitely non-standard. Registers are non-standard. How about stating basic information, like compiler (Turbo C?) and OS (WinXP?) and processor (Intel 32 bit?).

You might try googling, perhaps for "c programming status register integer overflow". The first hit is
http://www.osdata.com/topic/language/asm/register.htm
[edit] From that page:

overflow Set if arithmetic overflow occurs. Used in Digital VAX [V], Intel 80x86 [OF], Motorola 680x0 [V], Motorola 68300 [V], Motorola M68HC16 [V].

As you can see, it's very processor-dependant.

It would be better to use one of the standard C methods outlined above if possible. [/edit]