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Noob question
Posted: October 26th, 2017, 10:57 am
by Raimond
Hello peeps, I'm at the snake tutorial right now, wish i had more time for tuts but for now i have one question.
i see chilli did something i can't fully understand and i wish you could help me.
when initializing the rng constructor
rng(std::random_device()()) he used 2 of "()", my question is why.
rng is from "std::mt19937 rng;"
Re: Noob question
Posted: October 26th, 2017, 4:00 pm
by chili
The first () constructs the random_device object, and the second () calls the function operator (the generator function) on that object.
Re: Noob question
Posted: October 26th, 2017, 6:57 pm
by albinopapa
If I do this:
Code: Select all
std::mt19937 rng( std::random_device()( ) );
I get the error "Function returning function is not allowed".
However, if I do it in a class initializer list:
Code: Select all
class MyClass
{
public:
MyClass()
:
rng( std::random_device()( ) )
{}
private:
std::mt19937 rng;
};
Everything builds fine.
If you create a temporary random number generator in a function, you must use braces to construct the random_device and parentheses to call the operator() ( generate function ).
Code: Select all
std::mt19937 rng( std::random_device{}( ) );
Re: Noob question
Posted: October 27th, 2017, 5:25 pm
by cameron
Think that's because compiler thinks you're declaring a function.