dimanche 17 juillet 2016

Lots of compiler errors when attempting to use random_device, mt19937, and uniform_int_distribution

I have only recently started learning C++, so I am having trouble debugging my program.

I want to generate random numbers. After some googling, it appears that one way to do that is something along the lines of

#include <random>

std::mt19937 rng;
std::uniform_int_distribution<int> distribution;

int main()
{
    rng(std::random_device()());
    distribution(0, 10);
}

However, when I compile that with g++ -std=c++14 test.cpp, I get these errors:

test.cpp: In function ‘int main()’:
test.cpp:8:31: error: no match for call to ‘(std::mt19937 {aka std::mersenne_twister_engine<unsigned int, 32u, 624u, 397u, 31u, 2567483615u, 11u, 4294967295u, 7u, 2636928640u, 15u, 4022730752u, 18u, 1812433253u>}) (std::random_device::result_type)’
     rng(std::random_device()());
                               ^
In file included from /usr/include/c++/5/random:49:0,
                 from test.cpp:1:
/usr/include/c++/5/bits/random.h:546:7: note: candidate: std::mersenne_twister_engine<_UIntType, __w, __n, __m, __r, __a, __u, __d, __s, __b, __t, __c, __l, __f>::result_type std::mersenne_twister_engine<_UIntType, __w, __n, __m, __r, __a, __u, __d, __s, __b, __t, __c, __l, __f>::operator()() [with _UIntType = unsigned int; unsigned int __w = 32u; unsigned int __n = 624u; unsigned int __m = 397u; unsigned int __r = 31u; _UIntType __a = 2567483615u; unsigned int __u = 11u; _UIntType __d = 4294967295u; unsigned int __s = 7u; _UIntType __b = 2636928640u; unsigned int __t = 15u; _UIntType __c = 4022730752u; unsigned int __l = 18u; _UIntType __f = 1812433253u; std::mersenne_twister_engine<_UIntType, __w, __n, __m, __r, __a, __u, __d, __s, __b, __t, __c, __l, __f>::result_type = unsigned int]
       operator()();
       ^
/usr/include/c++/5/bits/random.h:546:7: note:   candidate expects 0 arguments, 1 provided
test.cpp:9:23: error: no match for call to ‘(std::uniform_int_distribution<int>) (int, int)’
     distribution(0, 10);
                       ^
In file included from /usr/include/c++/5/random:49:0,
                 from test.cpp:1:
/usr/include/c++/5/bits/random.h:1768:2: note: candidate: template<class _UniformRandomNumberGenerator> std::uniform_int_distribution<_IntType>::result_type std::uniform_int_distribution<_IntType>::operator()(_UniformRandomNumberGenerator&) [with _UniformRandomNumberGenerator = _UniformRandomNumberGenerator; _IntType = int]
  operator()(_UniformRandomNumberGenerator& __urng)
  ^
/usr/include/c++/5/bits/random.h:1768:2: note:   template argument deduction/substitution failed:
test.cpp:9:23: note:   candidate expects 1 argument, 2 provided
     distribution(0, 10);
                       ^
In file included from /usr/include/c++/5/random:49:0,
                 from test.cpp:1:
/usr/include/c++/5/bits/random.h:1773:2: note: candidate: template<class _UniformRandomNumberGenerator> std::uniform_int_distribution<_IntType>::result_type std::uniform_int_distribution<_IntType>::operator()(_UniformRandomNumberGenerator&, const std::uniform_int_distribution<_IntType>::param_type&) [with _UniformRandomNumberGenerator = _UniformRandomNumberGenerator; _IntType = int]
  operator()(_UniformRandomNumberGenerator& __urng,
  ^
/usr/include/c++/5/bits/random.h:1773:2: note:   template argument deduction/substitution failed:
test.cpp:9:23: note:   cannot convert ‘10’ (type ‘int’) to type ‘const std::uniform_int_distribution<int>::param_type&’
     distribution(0, 10);
                       ^

I did some research into random_device, mt19937, and uniform_int_distribution, and with my limited knowledge it appears that I'm using everything correctly. I also basically copy-pasted the code from other answers here on SO, so it seems like the code should work. Did changing the context of the code break something?




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