So, every time I am developing something big, with multiple modules coming together to build a final functionality, I've been wondering the same question: Where to initialize the random seed if more than 1 module needs to use the random function?
If I have a certain class that needs random (e.g. class that initializes itself by sorting an input array with self-implemented quicksort, so I would need a random for the pivot choice), I usually have a private static bool isRandOn; variable, so before I start the random pivot choice, I check that variable and do srand(time(NULL)); if the random is not on yet.
If I have a ton of utility functions in a namespace, I do a very similar thing: I put such a variable in an anonymous namespace inside my utils library, and do the more-or-less same thing as with a class.
The problem I have is when combining those modules. All by it self, I know each module will not set the seed more than once. But, I want to be able to use a various amount of my modules together, I want other people to be able to use one or more of my modules independent of the others...
So, what is the best way to handle multiple random-seed-needing modules? Set the seed in each module? Do not set the seed at all but instead document the usage of random and make the user initialize the seed if he wants to use the module? Something third?
I would suggest using Boost.Random rather than relying on some global state shared at the program level.
Boost.Random has two concepts:
Each module may then have its own Engine, or indeed several of them: there is no specific reason for a given Engine to be shared between several different functions within the same module.
As a final word: whatever you do make sure you have a way to set the seed(s) deterministically for bug repro purposes. Bug repro may benefit from having multiple engines (isolation of the parts helps).