kwh@bentley.UUCP (KW Heuer) (03/26/86)
In article <4336@dartvax.UUCP> dartvax!davidk (David C. Kovar) writes: >>That's easy. Just insert a "srand(getpid());" somewhere in the beginning >>of the program, before the first "rand" call. > >That'll still have the same problem. getpid() will return the same pid >each time the same user runs it, thus you would get the same seed for >rand each time. Try srand(time()); instead. [0] You seem to be confusing getpid() with getuid(). On UNIX[tm], you get a new process each time you run the program, so getpid() will return a unique identifier. On some non-UNIX systems (with no fork/exec) you may get the same ID each time. [1] time() expects an argument. You need "time((long *)0)". [2] time() returns a long. It must be declared as such. [3] srand() expects an int. The result of time() must be cast. (IMPORTANT: effects [2] and [3] do NOT cancel out if you ignore both!) [4] I once ran the same program twice within one second (the resolution of the UNIX clock) and got the same seed. Since then I've always used both time() and getpid(), which seems to be a reasonable idea. (Messy? Well, it's only done once per program!) (I wish srand(0) would do this automatically! Summary: extern long time(); ... srand((int)time((long *)0) + getpid());