problems generating 32 bit random numbers

Question

I want to generate a random number between specified range, but when i run the following code. it gives error , can any one explain the error please?

#include <iostream> #include <random> using namespace std; unsigned long int starting=2347483648; unsigned long int ending=3994967296; unsigned int rand(unsigned long int first,unsigned long int last) { std::random_device rd; std::mt19937 eng(rd()); std::uniform_int_distribution<> distr(first, last); return (unsigned int)distr(eng) << ' '; } int main() { cout<<rand(1,ending);//generate random number in this range }

The program breaks and gives an error

invalid min and max arguments for uniform_int

Explain the reason of error and tell me how can i generate the random numbers between the above specified range

If I'm not wrong, the default template argument for uniform_int_distribution is an int. And an unsigned long int cannot fit into an int. — user1508519
– user1508519, Commented Jan 13, 2014 at 17:44
well if the above function is called with these values rand(starting,ending), it works fine... — Ahmed
– Ahmed, Commented Jan 13, 2014 at 17:47
i didn't understand @fleetC0m ...... i didn't mean anything like that...just here for learning — Ahmed
– Ahmed, Commented Jan 13, 2014 at 18:01
I don't see why the downvotes. This problem could trip anybody up if they weren't familiar with uniform_int_distribution. — user1508519
– user1508519, Commented Jan 13, 2014 at 18:02

score 3 · Accepted Answer · 2014-01-13 17:57:50Z

Try this:

 std::uniform_int_distribution<unsigned long int> distr(first, last); return (unsigned int)distr(eng); }

I also removed the errorneous << ' ' which is left-shifting with an space character, rather than appending a space to the output.

int main() { cout<<rand(1,ending) << " "; }

When ending (or last) is converted into an int, it becomes -300000000. ending also becomes max() for distr, so ending == distr.max(). Using std::numeric_limits<int>::min(), we can see that the resulting value can fit into an int.

Yes it works but can you explain why the above code gives error if first argument is 1 and runs if it is "starting"

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