Thread: Type Promotion in function call

  1. #1
    Registered User rogster001's Avatar
    Join Date
    Aug 2006
    Liverpool UK

    Type Promotion in function call

    I have not compiled this just looking for advice:

    unsigned functionFoo()
    	unsigned fooNum = 0;
    	return fooNum;
    void functionBar(unsigned long myNum)
    int main()
    	unsigned num = functionFoo();
    	return 0;
    So is this safe? Its is for a random number generator, so i would like to be sure everything is tickety-boo, it's using Prelude's mersenne twister implementation, the seed function takes the unsigned long int, but prior to that i am using a seperate time_t hash function that returns the unsigned int
    Thought for the day:
    "Are you sure your sanity chip is fully screwed in sir?" (Kryten)
    FLTK: "The most fun you can have with your clothes on."

    "If I had thought of it and had some marketing sense every computer and just about any gadget would have had a little 'C++ Inside' sticker on it'"

  2. #2
    Cat without Hat CornedBee's Avatar
    Join Date
    Apr 2003
    It's safe in that conversion from unsigned int -> unsigned long is guaranteed to be lossless. It may be unsafe in that it may make the outcome of the rng more predictable than necessary (if long is actually larger than int, you're not using the full range of the seed), but that's unlikely to be a serious problem.
    All the buzzt!

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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