What is the best way to seed srand()?

c random srand
Matt picture Matt · Apr 6, 2013 · Viewed 14.1k times · Source

The way I learned was to initially seed the random number generator with srand(time(NULL)) and then use calls to rand() to generate random numbers. The problem with this approach is if I run my program multiple times in the same second, the random numbers generated will always be the same. What is a good way around this?

Answer

R.. GitHub STOP HELPING ICE picture R.. GitHub STOP HELPING ICE · Apr 6, 2013

On POSIX systems, use clock_gettime to get the current time in nanoseconds. If you don't need a lot of bits, you can just forget the PRNG and use the low-order bits of the time as your random number directly. :-)

Related questions

How to use function srand() with time.h?

My program contains code that should generate a random positive integer number every time I execute it. It generates random numbers but only once. After that, when I execute same code, it gives me same values, and it is making …

Read More
srand() — why call it only once?

This question is about a comment in this question Recommended way to initialize srand? The first comment says that srand() should be called only ONCE in an application. Why is it so?

Read More
How does srand relate to rand function?

I understand that rand() function generates the same number(s) each you run it if you don't change the seed number. That's where srand() comes in. Time is always changing so I know that you should pass the time(null) …

Read More