[英]How to make a member function of a class in C++ generate a different random number each time it is called?
I have a class which also includes a random number engine and its distribution: 我有一堂课,其中还包括一个随机数引擎及其分布:
#include <iostream>
#include <cmath>
#include <random>
#include <chrono>
class C
{
public:
typedef std::mt19937_64 engine;
typedef std::uniform_real_distribution<double> distribution;
.
.
.
protected:
engine rng;
distribution dist;
void func();
.
.
.
};
Since the constructor is called only once, I put the seed in it: 由于构造函数仅被调用一次,因此将种子放入其中:
C::C()
{ .
.
.
unsigned seed = std::chrono::system_clock::now().time_since_epoch().count();
distribution dist(0.0, pow(10,12));
engine rng(seed);
}
The following member function is supposed to generate a random number and is going to be called lots of times in a single run of the program: 以下成员函数应该生成一个随机数,并且在程序的一次运行中将被多次调用:
void C::func()
{ .
.
.
double randNum = floor(dist(rng));
std::cout << randNum << std::endl;
.
.
.
}
However, each time it generates the number 0 as the random number. 但是,每次生成数字0作为随机数。 It seems that dist(rng)
is not doing its job. 似乎dist(rng)
并未完成其工作。
I really need to find the problem and correct the output. 我真的需要找到问题并更正输出。 I would appreciate any help. 我将不胜感激任何帮助。
You define your dist
and eng
variables in the class 您可以在类中定义dist
和eng
变量
protected:
engine rng;
distribution dist; // Here
void func();
And in the constructor you define another with the same name 然后在构造函数中定义另一个同名
C::C()
{ .
.
.
unsigned seed = std::chrono::system_clock::now().time_since_epoch().count();
distribution dist(0.0, pow(10,12)); // Here
engine rng(seed);
}
I assume you want the latter to be an assignment, not a new variable. 我假设您希望后者是一个赋值,而不是一个新变量。 Then you will get the numbers you want. 然后,您将获得所需的号码。
C::C()
{ .
.
.
unsigned seed = std::chrono::system_clock::now().time_since_epoch().count();
dist = distribution(0.0, pow(10,12)); // Here
rng = engine(seed);
}
Or with initialization 或初始化
C() : dist(0.0, pow(10, 12)),
rng(std::chrono::system_clock::now().time_since_epoch().count())
Sami is close, but you should really be initialising these members: 萨米(Sami)接近,但您应该真正初始化这些成员:
C::C()
: dist(0.0, pow(10, 12))
, rng(std::chrono::system_clock::now().time_since_epoch().count())
{}
In the constructor, you're creating a local variable dist
that hides the class member, while the class member gets default-initialized. 在构造函数中,您要创建一个局部变量dist
,该变量将隐藏类成员,而该类成员将被默认初始化。 A default-initialized uniform_real_distribution
generates values in the range [0,1), which floor
will always turn into 0. 默认初始化的uniform_real_distribution
生成[0,1)范围内的值,该floor
将始终变为0。
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