C++：隨機數產生器(random-number generator) 詳解

隨機數, C語言的函數是rand(), C++則是隨機數產生器(random-number generator) = 分布對象(distribution object) + 引擎(engine);

使函數每次產生不同的隨機數, 需要使用靜態(static)局部變數, 這樣分布對象和引擎就能保持(hold)狀態(state), 每次都產生一個新的;

產生隨機的整數, 使用分布對象uniform_int_distribution<>, 預設範本參數是int;

產生隨機的浮點數, 使用分布對象uniform_real_distribution<>, 預設範本參數是double;

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代碼:

#include <iostream>  #include <vector>  #include <string>  #include <random>              using namespace std;        std::vector<unsigned> good_randVec()  {      static std::default_random_engine e; //靜態      static std::uniform_int_distribution<unsigned> u(0,9); //靜態      std::vector<unsigned> ret;      for(size_t i=0; i<10; ++i)          ret.push_back(u(e));      return ret;  }        int main()  {      std::default_random_engine e;      std::cout << "engine : ";      for(size_t i=0; i<10; ++i)          std::cout << e() << " ";      std::cout << std::endl;            std::cout << "uniform : ";      std::uniform_int_distribution<unsigned> u(0, 9); //即[0, 9]      for(size_t i=0; i<10; ++i)          std::cout << u(e) << " ";      std::cout << std::endl;            std::cout << "min : " << e.min() << " max : " << e.max() << std::endl;            std::vector<unsigned> v1(good_randVec());      std::vector<unsigned> v2(good_randVec());      for(size_t i=0; i<v1.size(); ++i)          std::cout << v1[i] << " ";      std::cout << std::endl;      for(size_t i=0; i<v2.size(); ++i)          std::cout << v2[i] << " ";      std::cout << std::endl;            std::uniform_real_distribution<double> ud(0, 1);      std::cout << "float : ";      for(size_t i=0; i<10; ++i)          std::cout << ud(e) << " ";      std::cout << std::endl;            return 0;  }

輸出:

engine : 16807 282475249 1622650073 984943658 1144108930 470211272 101027544 1457850878 1458777923 2007237709   uniform : 3 5 8 0 0 5 6 0 3 0   min : 1 max : 2147483646  0 1 7 4 5 2 0 6 6 9   3 5 8 0 0 5 6 0 3 0   float : 0.686773 0.930436 0.526929 0.653919 0.701191 0.762198 0.0474645 0.328234 0.75641 0.365339

作者：csdn部落格 Spike_King