Random numbers - seeding needed?

I noticed that mt_rand() still works perfectly when I don't seed the generator. Is seeding really needed?

It works perfectly without seeding? I doubt that.

The rand() functions create their "random" numbers based on a "seed" if the "seed" is the same, the generated sequence will be the same.

So to ensure that you get "random" numbers you must make sure the seed is different every time (which is why microtime() is used)

I'm not contradicting you, but go to the following test file I made and see the result of an unseeded mt_rand() for yourself:

or go to:

to see the source code.

Linus

Indeed, it seems to be seeded automatically by PHP.

But, the manual does not mention what it is seeded with, so it's still good idea to seed it manually.